Today if we detect concurrent modification of a snapshot repository then we mark it with `CORRUPTED_REPO_GEN` which blocks further writes to try and prevent additional damage to its contents. You can remove the marker by calling the register-repository API again, but this API will discard no-op re-registrations without taking any action. You can work around this by unregistering the repository first (which may be impossible if it's still in use for searchable snapshots) or by re-registering it with some trivial setting change (which seems hacky).

We should not consider it a no-op re-registration if the repository is currently marked with `CORRUPTED_REPO_GEN`, because doing this re-registration will re-read the repo contents and clear the corruption marker and therefore is not a no-op.
server/src/internalClusterTest/java/org/elasticsearch/snapshots/ConcurrentSnapshotsIT.java
client().admin()
                        .cluster()
                        .prepareCloneSnapshot(repository, "snapshot-" + i, "clone-" + i)
                        .setIndices("index-" + i)
                        .execute()
                );
            }
        }
        
        final List<ActionFuture<AcknowledgedResponse>> deleteFutures = new ArrayList<>(nbIndices);
        for (int i = 0; i < nbIndices; i++) {
            deleteFutures.add(startDeleteSnapshot(repository, "snapshot-" + i));
        }
        for (ActionFuture<RestoreSnapshotResponse> operation : restoreFutures) {
            try {
                final RestoreInfo restoreResponse = operation.get().getRestoreInfo();
                assertThat(restoreResponse.successfulShards(), greaterThanOrEqualTo(1));
                assertEquals(0, restoreResponse.failedShards());
            } catch (ExecutionException e) {
                final Throwable csee = ExceptionsHelper.unwrap(e, ConcurrentSnapshotExecutionException.class);
                assertThat(csee, instanceOf(ConcurrentSnapshotExecutionException.class));
            }
        }
        for (ActionFuture<AcknowledgedResponse> operation : cloneFutures) {
            try {
                assertAcked(operation.get());
            } catch (ExecutionException e) {
                final Throwable csee = ExceptionsHelper.unwrap(e, SnapshotException.class);
                assertThat(
                    csee,