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
internalCluster().setDisruptionScheme(networkDisruption);
        final List<String> snapshotNames = createNSnapshots(repoName, randomIntBetween(2, 5));
        final String masterName = internalCluster().getMasterName();
        blockMasterFromDeletingIndexNFile(repoName);
        final ActionFuture<CreateSnapshotResponse> snapshotOther = startFullSnapshotFromMasterClient(repoName, "snap-other");
        waitForBlock(masterName, repoName);
        final String snapshotOne = snapshotNames.get(0);
        final ActionFuture<AcknowledgedResponse> deleteSnapshotOne = startDeleteSnapshot(repoName, snapshotOne);
        awaitNDeletionsInProgress(1);
        networkDisruption.startDisrupting();
        ensureStableCluster(3, dataNode);
        unblockNode(repoName, masterName);
        networkDisruption.stopDisrupting();
        ensureStableCluster(4);
        assertSuccessful(snapshotOther);
        try {
            deleteSnapshotOne.actionGet();
        } catch (RepositoryException re) {
            
        } catch (SnapshotMissingException re) {
            
            
        }
        awaitNoMoreRunningOperations();
    }
    public void testMasterFailoverDuringStaleIndicesCleanup() throws Exception {
        internalCluster().startMasterOnlyNodes(3);
        final String dataNode = internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");