diff --git a/backend/alembic/versions/2026-08-24_e7b2c94a63d1_username_changes_enabled.py b/backend/alembic/versions/2026-08-24_e7b2c94a63d1_username_changes_enabled.py
new file mode 100644
index 0000000..e6f6429
--- /dev/null
+++ b/backend/alembic/versions/2026-08-24_e7b2c94a63d1_username_changes_enabled.py
@@ -0,0 +1,38 @@
+"""username_changes_enabled — site toggle for self-service renames (#298)
+
+Adds ``site_settings.username_changes_enabled``: whether accounts may rename
+themselves from the profile page. Server default TRUE, so existing installs
+keep today's behaviour and nothing is backfilled. Off gates only the
+self-service route — an admin rename (manage_users) is unaffected.
+
+Revision ID: e7b2c94a63d1
+Revises: d1a6b83f47c2
+Create Date: 2026-08-24
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "e7b2c94a63d1"
+down_revision = "d1a6b83f47c2"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    with op.batch_alter_table("site_settings") as batch:
+        batch.add_column(
+            sa.Column(
+                "username_changes_enabled",
+                sa.Boolean(),
+                nullable=False,
+                server_default=sa.true(),
+            )
+        )
+
+
+def downgrade() -> None:
+    with op.batch_alter_table("site_settings") as batch:
+        batch.drop_column("username_changes_enabled")
diff --git a/backend/models/site_settings.py b/backend/models/site_settings.py
index 9c4ef0b..4fb4179 100644
--- a/backend/models/site_settings.py
+++ b/backend/models/site_settings.py
@@ -93,6 +93,12 @@ class SiteSettings(Base, TimestampMixin):
     registration_open: Mapped[bool] = mapped_column(
         Boolean, nullable=False, default=True, server_default="1"
     )
+    # Whether accounts may rename themselves from the profile page (#298). Off
+    # pins usernames to what was provisioned — only the self-service path is
+    # gated; manage_users holders can always rename from Admin → Users.
+    username_changes_enabled: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=True, server_default="1"
+    )
     # Outbound SMTP for the send_email automation action (§5.3). When smtp_host
     # is set these override the env config; unset = fall back to env (or, if that
     # too is unset, email is a logged no-op).
diff --git a/backend/routers/auth.py b/backend/routers/auth.py
index e0c4a81..0855f21 100644
--- a/backend/routers/auth.py
+++ b/backend/routers/auth.py
@@ -536,6 +536,16 @@ async def change_username(
             status_code=status.HTTP_429_TOO_MANY_REQUESTS,
             detail="Too many attempts — please wait a few minutes and try again",
         )
+    # Site policy gate (#298), before the password check so a disabled endpoint
+    # never verifies passwords. Only this self-service path is governed — an
+    # admin rename (manage_users, routers/users.py) is how a provisioned name
+    # gets fixed while renames are off.
+    site = await db.get(SiteSettings, SITE_SETTINGS_ID)
+    if site is not None and not site.username_changes_enabled:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Username changes are disabled on this platform",
+        )
     if not verify_password(body.current_password, current_user.password_hash):
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
diff --git a/backend/routers/site_settings.py b/backend/routers/site_settings.py
index 1019797..521441d 100644
--- a/backend/routers/site_settings.py
+++ b/backend/routers/site_settings.py
@@ -372,6 +372,7 @@ def _operational_out(
 ) -> OperationalSettingsOut:
     return OperationalSettingsOut(
         registration_open=settings.registration_open,
+        username_changes_enabled=settings.username_changes_enabled,
         smtp_host=settings.smtp_host,
         smtp_port=settings.smtp_port,
         smtp_username=settings.smtp_username,
@@ -423,6 +424,9 @@ async def update_operational_settings(
         )
     settings = await get_or_create_settings(db)
     settings.registration_open = body.registration_open
+    # Omitted = unchanged (#298), the update_checks_enabled pattern below.
+    if body.username_changes_enabled is not None:
+        settings.username_changes_enabled = body.username_changes_enabled
     settings.smtp_host = body.smtp_host or None
     settings.smtp_port = body.smtp_port
     settings.smtp_username = body.smtp_username or None
diff --git a/backend/schemas/site_settings.py b/backend/schemas/site_settings.py
index 99b79c8..99f866b 100644
--- a/backend/schemas/site_settings.py
+++ b/backend/schemas/site_settings.py
@@ -90,6 +90,10 @@ class SiteSettingsOut(BaseModel):
     # (issue #74). Public so the join button / profile banner can explain a
     # 403 without a round-trip to admin-only settings.
     email_verification_enabled: bool = False
+    # Whether accounts may rename themselves (#298). Public so the profile page
+    # can hide its username card without an admin-only round-trip; a policy
+    # bit, not infrastructure detail.
+    username_changes_enabled: bool = True
 
 
 class SiteSettingsUpdate(BaseModel):
@@ -143,6 +147,8 @@ class OperationalSettingsOut(BaseModel):
     model_config = ConfigDict(from_attributes=True)
 
     registration_open: bool
+    # Self-service rename toggle (#298); admin rename is never gated by it.
+    username_changes_enabled: bool
     smtp_host: str | None
     smtp_port: int
     smtp_username: str | None
@@ -191,6 +197,11 @@ class BackupImportRequest(BaseModel):
 
 class OperationalSettingsUpdate(BaseModel):
     registration_open: bool
+    # Self-service rename toggle (#298). **Omitted / null = leave unchanged**,
+    # the update_checks_enabled pattern below: this PUT replaces the whole
+    # object, and a `= True` default would let a scripted client that tweaks
+    # SMTP and omits this field silently re-enable renames an admin turned off.
+    username_changes_enabled: bool | None = None
     smtp_host: str | None = Field(default=None, max_length=255)
     smtp_port: int = Field(default=587, ge=1, le=65535)
     smtp_username: str | None = Field(default=None, max_length=255)
diff --git a/backend/tests/test_site_settings.py b/backend/tests/test_site_settings.py
index 6ae981b..5f335d3 100644
--- a/backend/tests/test_site_settings.py
+++ b/backend/tests/test_site_settings.py
@@ -38,6 +38,7 @@ async def test_public_read_returns_defaults_without_auth(client):
         "archive_retention_days": 30,
         "email_required": False,
         "email_verification_enabled": False,
+        "username_changes_enabled": True,
     }
     # Public shape only — no internal fields leak.
     assert "updated_at" not in body
@@ -73,6 +74,7 @@ async def test_admin_update_round_trips(client):
         "archive_retention_days": 30,
         "email_required": False,
         "email_verification_enabled": False,
+        "username_changes_enabled": True,
     }
 
 
diff --git a/backend/tests/test_username_change.py b/backend/tests/test_username_change.py
index e6c0302..e2e1478 100644
--- a/backend/tests/test_username_change.py
+++ b/backend/tests/test_username_change.py
@@ -12,6 +12,7 @@
 
 from db import SessionLocal, utcnow
 from models.audit_log import AuditLogEntry
+from models.site_settings import SITE_SETTINGS_ID, SiteSettings
 from models.user import USERNAME_CHANGE_COOLDOWN, User
 from tests.conftest import admin_token
 
@@ -167,3 +168,89 @@ async def test_admin_rename_bypasses_cooldown_and_audits_actor(client):
     admin_entry = next(e for e in entries if e.payload["actor_user_id"] == admin_id)
     assert admin_entry.payload["old_name"] == "rowdy2"
     assert admin_entry.payload["new_name"] == "clean-name"
+
+
+# --- site toggle: username_changes_enabled (#298) ----------------------------
+
+
+async def _set_username_changes(enabled: bool) -> None:
+    """Flip the site policy directly — the API round-trip has its own test."""
+    async with SessionLocal() as session:
+        settings = await session.get(SiteSettings, SITE_SETTINGS_ID)
+        if settings is None:
+            settings = SiteSettings(id=SITE_SETTINGS_ID)
+            session.add(settings)
+        settings.username_changes_enabled = enabled
+        await session.commit()
+
+
+async def test_disabled_blocks_self_service_before_the_password_check(client):
+    token, _ = await _register(client, "pinned")
+    await _set_username_changes(False)
+
+    resp = await _change(client, token, "renamed")
+    assert resp.status_code == 403
+    assert "disabled" in resp.json()["detail"].lower()
+
+    # The gate sits before password verification: a wrong password while
+    # disabled is still a 403, not a 400 — the endpoint never checks it.
+    wrong_pw = await _change(client, token, "renamed", pw="not-my-password")
+    assert wrong_pw.status_code == 403
+
+    me = await client.get("/api/auth/me", headers=_auth(token))
+    assert me.json()["display_name"] == "pinned"  # unchanged
+
+
+async def test_disabled_still_allows_admin_rename(client):
+    _, user_id = await _register(client, "issued-name")
+    await _set_username_changes(False)
+
+    admin = await admin_token(client)
+    resp = await client.patch(
+        f"/api/users/{user_id}",
+        json={"display_name": "corrected-name"},
+        headers=_auth(admin),
+    )
+    assert resp.status_code == 200, resp.text
+    assert resp.json()["display_name"] == "corrected-name"
+
+
+async def test_reenabling_restores_self_service(client):
+    token, _ = await _register(client, "flippy")
+    await _set_username_changes(False)
+    assert (await _change(client, token, "flippy2")).status_code == 403
+
+    await _set_username_changes(True)
+    resp = await _change(client, token, "flippy2")
+    assert resp.status_code == 200, resp.text
+    assert resp.json()["display_name"] == "flippy2"
+
+
+async def test_flag_is_public_and_operational_put_roundtrips(client):
+    # Default: on, and visible on the public payload (the profile page hides
+    # its card off this, pre-fetching no admin-only endpoint).
+    public = await client.get("/api/site-settings")
+    assert public.json()["username_changes_enabled"] is True
+
+    admin = await admin_token(client)
+    # Turn it off through the admin surface.
+    off = await client.put(
+        "/api/site-settings/operational",
+        json={"registration_open": True, "username_changes_enabled": False},
+        headers=_auth(admin),
+    )
+    assert off.status_code == 200, off.text
+    assert off.json()["username_changes_enabled"] is False
+    assert (await client.get("/api/site-settings")).json()[
+        "username_changes_enabled"
+    ] is False
+
+    # Omitting the field leaves it unchanged (the update_checks_enabled
+    # omission contract) — a scripted PUT must not silently re-enable it.
+    omitted = await client.put(
+        "/api/site-settings/operational",
+        json={"registration_open": True},
+        headers=_auth(admin),
+    )
+    assert omitted.status_code == 200, omitted.text
+    assert omitted.json()["username_changes_enabled"] is False
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index b67d0b7..eddbb48 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -2140,6 +2140,11 @@
       "publicSignup": "Public sign-up",
       "signupOpen": "Open — anyone can register",
       "signupClosed": "Closed — invite / admin-created only",
+      "usernameChanges": "Username changes",
+      "usernameChangesDescription": "Whether accounts can rename themselves from the profile page (subject to the rename cooldown). Off pins usernames to what was issued — an administrator can still rename any account from Admin → Users.",
+      "selfServiceRenames": "Self-service username changes",
+      "renamesOn": "On — users may rename themselves",
+      "renamesOff": "Off — usernames are fixed; only admins rename",
       "updateChecks": "Update checks",
       "updateChecksDescription": "Once a day Flagpost asks <mono>updates.flagpost.io</mono> whether a newer release exists. The request sends <strong>only the version you're running</strong> — no identifier, no hostname, no competition or user data — and the count of those requests is how the project gauges how many deployments are live. See <link>PRIVACY.md</link> for the full detail.",
       "checkForUpdates": "Check for updates",
diff --git a/frontend/messages/es.json b/frontend/messages/es.json
index f71cf7c..dd633cd 100644
--- a/frontend/messages/es.json
+++ b/frontend/messages/es.json
@@ -2140,6 +2140,11 @@
       "publicSignup": "Public sign-up",
       "signupOpen": "Open — anyone can register",
       "signupClosed": "Closed — invite / admin-created only",
+      "usernameChanges": "Username changes",
+      "usernameChangesDescription": "Whether accounts can rename themselves from the profile page (subject to the rename cooldown). Off pins usernames to what was issued — an administrator can still rename any account from Admin → Users.",
+      "selfServiceRenames": "Self-service username changes",
+      "renamesOn": "On — users may rename themselves",
+      "renamesOff": "Off — usernames are fixed; only admins rename",
       "updateChecks": "Update checks",
       "updateChecksDescription": "Once a day Flagpost asks <mono>updates.flagpost.io</mono> whether a newer release exists. The request sends <strong>only the version you're running</strong> — no identifier, no hostname, no competition or user data — and the count of those requests is how the project gauges how many deployments are live. See <link>PRIVACY.md</link> for the full detail.",
       "checkForUpdates": "Check for updates",
diff --git a/frontend/messages/fr.json b/frontend/messages/fr.json
index 42a5b54..57c77f5 100644
--- a/frontend/messages/fr.json
+++ b/frontend/messages/fr.json
@@ -2140,6 +2140,11 @@
       "publicSignup": "Public sign-up",
       "signupOpen": "Open — anyone can register",
       "signupClosed": "Closed — invite / admin-created only",
+      "usernameChanges": "Username changes",
+      "usernameChangesDescription": "Whether accounts can rename themselves from the profile page (subject to the rename cooldown). Off pins usernames to what was issued — an administrator can still rename any account from Admin → Users.",
+      "selfServiceRenames": "Self-service username changes",
+      "renamesOn": "On — users may rename themselves",
+      "renamesOff": "Off — usernames are fixed; only admins rename",
       "updateChecks": "Update checks",
       "updateChecksDescription": "Once a day Flagpost asks <mono>updates.flagpost.io</mono> whether a newer release exists. The request sends <strong>only the version you're running</strong> — no identifier, no hostname, no competition or user data — and the count of those requests is how the project gauges how many deployments are live. See <link>PRIVACY.md</link> for the full detail.",
       "checkForUpdates": "Check for updates",
diff --git a/frontend/messages/pl.json b/frontend/messages/pl.json
index 1b62e75..c7b16f5 100644
--- a/frontend/messages/pl.json
+++ b/frontend/messages/pl.json
@@ -2140,6 +2140,11 @@
       "publicSignup": "Public sign-up",
       "signupOpen": "Open — anyone can register",
       "signupClosed": "Closed — invite / admin-created only",
+      "usernameChanges": "Username changes",
+      "usernameChangesDescription": "Whether accounts can rename themselves from the profile page (subject to the rename cooldown). Off pins usernames to what was issued — an administrator can still rename any account from Admin → Users.",
+      "selfServiceRenames": "Self-service username changes",
+      "renamesOn": "On — users may rename themselves",
+      "renamesOff": "Off — usernames are fixed; only admins rename",
       "updateChecks": "Update checks",
       "updateChecksDescription": "Once a day Flagpost asks <mono>updates.flagpost.io</mono> whether a newer release exists. The request sends <strong>only the version you're running</strong> — no identifier, no hostname, no competition or user data — and the count of those requests is how the project gauges how many deployments are live. See <link>PRIVACY.md</link> for the full detail.",
       "checkForUpdates": "Check for updates",
diff --git a/frontend/src/app/(app)/admin/settings/page.tsx b/frontend/src/app/(app)/admin/settings/page.tsx
index 026615a..368bf3c 100644
--- a/frontend/src/app/(app)/admin/settings/page.tsx
+++ b/frontend/src/app/(app)/admin/settings/page.tsx
@@ -241,6 +241,7 @@ function SettingsForm({
   const t = useTranslations("admin.settings");
   const update = useUpdateOperationalSettings();
   const [registrationOpen, setRegistrationOpen] = useState(data.registration_open);
+  const [usernameChanges, setUsernameChanges] = useState(data.username_changes_enabled);
   const [updateChecks, setUpdateChecks] = useState(data.update_checks_enabled);
   const [host, setHost] = useState(data.smtp_host ?? "");
   const [port, setPort] = useState(String(data.smtp_port));
@@ -317,6 +318,7 @@ function SettingsForm({
     update.mutate(
       {
         registration_open: registrationOpen,
+        username_changes_enabled: usernameChanges,
         smtp_host: host.trim() || null,
         smtp_port: Number(port) || 587,
         smtp_username: username.trim() || null,
@@ -369,6 +371,27 @@ function SettingsForm({
           </CardContent>
         </Card>
 
+        <Card>
+          <CardHeader>
+            <CardTitle>{t("usernameChanges")}</CardTitle>
+            <CardDescription>{t("usernameChangesDescription")}</CardDescription>
+          </CardHeader>
+          <CardContent>
+            <div className="grid gap-2">
+              <Label htmlFor="username-changes">{t("selfServiceRenames")}</Label>
+              <Select
+                id="username-changes"
+                value={usernameChanges ? "on" : "off"}
+                onChange={(e) => setUsernameChanges(e.target.value === "on")}
+                className="max-w-xs"
+              >
+                <option value="on">{t("renamesOn")}</option>
+                <option value="off">{t("renamesOff")}</option>
+              </Select>
+            </div>
+          </CardContent>
+        </Card>
+
         <Card>
           <CardHeader>
             <CardTitle>{t("updateChecks")}</CardTitle>
diff --git a/frontend/src/components/profile/username-card.test.tsx b/frontend/src/components/profile/username-card.test.tsx
index 2fd3d8b..d13f5ca 100644
--- a/frontend/src/components/profile/username-card.test.tsx
+++ b/frontend/src/components/profile/username-card.test.tsx
@@ -26,10 +26,19 @@ vi.mock("@/stores/auth", () => ({
 vi.mock("@/lib/hooks/use-users", () => ({
   useChangeUsername: () => ({ mutate: vi.fn(), isPending: false }),
 }));
+// Site policy (#298): the card reads only `username_changes_enabled` off the
+// public settings; default it on so the pre-existing tests are unaffected.
+let usernameChangesEnabled = true;
+vi.mock("@/lib/hooks/use-site-settings", () => ({
+  useSiteSettings: () => ({
+    data: { username_changes_enabled: usernameChangesEnabled },
+  }),
+}));
 vi.mock("@/stores/toast", () => ({ toast: vi.fn() }));
 
 describe("UsernameCard", () => {
   it("shows the change form when no cooldown is active", () => {
+    usernameChangesEnabled = true;
     current = { ...base, username_change_allowed_at: null };
     renderWithIntl(<UsernameCard />);
     expect(screen.getByLabelText("Username")).toHaveValue("ada");
@@ -37,10 +46,18 @@ describe("UsernameCard", () => {
   });
 
   it("hides the form and shows the dated notice during the cooldown", () => {
+    usernameChangesEnabled = true;
     const future = new Date(Date.now() + 20 * 864e5).toISOString();
     current = { ...base, username_change_allowed_at: future };
     renderWithIntl(<UsernameCard />);
     expect(screen.queryByLabelText("Username")).toBeNull();
     expect(screen.getByText(/change it again on/i)).toBeInTheDocument();
   });
+
+  it("renders nothing at all when the site has renames disabled (#298)", () => {
+    usernameChangesEnabled = false;
+    current = { ...base, username_change_allowed_at: null };
+    const { container } = renderWithIntl(<UsernameCard />);
+    expect(container).toBeEmptyDOMElement();
+  });
 });
diff --git a/frontend/src/components/profile/username-card.tsx b/frontend/src/components/profile/username-card.tsx
index 9178e64..2d3cd31 100644
--- a/frontend/src/components/profile/username-card.tsx
+++ b/frontend/src/components/profile/username-card.tsx
@@ -19,6 +19,7 @@ import {
 } from "@/components/ui/card";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
+import { useSiteSettings } from "@/lib/hooks/use-site-settings";
 import { useChangeUsername } from "@/lib/hooks/use-users";
 import { useAuthStore } from "@/stores/auth";
 import { toast } from "@/stores/toast";
@@ -26,11 +27,15 @@ import { toast } from "@/stores/toast";
 export function UsernameCard() {
   const t = useTranslations("profile.username");
   const user = useAuthStore((s) => s.user);
+  const site = useSiteSettings();
   const change = useChangeUsername();
   const [name, setName] = useState(user?.display_name ?? "");
   const [password, setPassword] = useState("");
 
   if (!user) return null;
+  // Site policy (#298): renames disabled ⇒ no card at all — the server 403s
+  // anyway, so offering the form would only manufacture a dead end.
+  if (site.data && !site.data.username_changes_enabled) return null;
 
   const allowedAt = user.username_change_allowed_at
     ? new Date(user.username_change_allowed_at)
diff --git a/frontend/src/lib/hooks/use-site-settings.ts b/frontend/src/lib/hooks/use-site-settings.ts
index d7d9a41..d25e7a1 100644
--- a/frontend/src/lib/hooks/use-site-settings.ts
+++ b/frontend/src/lib/hooks/use-site-settings.ts
@@ -39,6 +39,7 @@ export const FALLBACK_SETTINGS: SiteSettings = {
   archive_retention_days: 30,
   email_required: false,
   email_verification_enabled: false,
+  username_changes_enabled: true,
 };
 
 /** Rewrite the backend-relative `logo_url` to the API origin so an `<img src>`
diff --git a/frontend/src/lib/types.ts b/frontend/src/lib/types.ts
index d685f09..3d95ab8 100644
--- a/frontend/src/lib/types.ts
+++ b/frontend/src/lib/types.ts
@@ -1156,6 +1156,9 @@ export interface SiteSettings {
   // Whether an unverified account is blocked from joining a competition
   // (#74). Public so the join button / profile banner can explain a 403.
   email_verification_enabled: boolean;
+  // Whether accounts may rename themselves (#298). Public so the profile page
+  // can hide its username card; admin rename is never gated by it.
+  username_changes_enabled: boolean;
 }
 
 // Admin shape adds the last-updated timestamp.
@@ -1166,6 +1169,8 @@ export interface SiteSettingsAdmin extends SiteSettings {
 /** Operational site config (Admin → Site settings): registration + SMTP. */
 export interface OperationalSettings {
   registration_open: boolean;
+  /** Self-service rename toggle (#298); admin rename is unaffected. */
+  username_changes_enabled: boolean;
   smtp_host: string | null;
   smtp_port: number;
   smtp_username: string | null;
@@ -1232,6 +1237,10 @@ export type BackupImportResult = Record<string, { created: number; skipped: numb
 
 export interface OperationalSettingsUpdate {
   registration_open: boolean;
+  /** Self-service rename toggle (#298). Omit to leave unchanged (the
+   *  update_checks_enabled pattern — a whole-object PUT must not silently
+   *  re-enable a feature an admin turned off). */
+  username_changes_enabled?: boolean;
   smtp_host: string | null;
   smtp_port: number;
   smtp_username: string | null;