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
public void testQueuedSnapshotOperationsAndBrokenRepoOnMasterFailOverMultipleRepos() throws Exception {
        disableRepoConsistencyCheck("This test corrupts the repository on purpose");
        internalCluster().startMasterOnlyNodes(3, LARGE_SNAPSHOT_POOL_SETTINGS);
        internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        final Path repoPath = randomRepoPath();
        createRepository(repoName, "mock", repoPath);
        createIndexWithContent("index-one");
        createNSnapshots(repoName, randomIntBetween(2, 5));
        final String masterNode = internalCluster().getMasterName();
        final String blockedRepoName = "repo-blocked";
        createRepository(blockedRepoName, "mock");
        createNSnapshots(blockedRepoName, randomIntBetween(1, 5));
        blockNodeOnAnyFiles(blockedRepoName, masterNode);
        final ActionFuture<AcknowledgedResponse> deleteFuture = startDeleteFromNonMasterClient(blockedRepoName, "*");
        waitForBlock(masterNode, blockedRepoName);
        awaitNDeletionsInProgress(1);
        final ActionFuture<CreateSnapshotResponse> createBlockedSnapshot = startFullSnapshotFromNonMasterClient(
            blockedRepoName,
            "queued-snapshot"
        );
        awaitNumberOfSnapshotsInProgress(1);
        final long generation = getRepositoryData(repoName).getGenId();
        blockNodeOnAnyFiles(repoName, masterNode);
        final ActionFuture<CreateSnapshotResponse> snapshotThree = startFullSnapshotFromNonMasterClient(repoName, "snapshot-three");
        waitForBlock(masterNode, repoName);
        awaitNumberOfSnapshotsInProgress(2);
        corruptIndexN(repoPath, generation);
        final ActionFuture<CreateSnapshotResponse> snapshotFour = startFullSnapshotFromNonMasterClient(repoName, "snapshot-four");
        awaitNumberOfSnapshotsInProgress(3);