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
final String masterName = internalCluster().startMasterOnlyNode();
        internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-test");
        createNSnapshots(repoName, randomIntBetween(1, 5));
        blockNodeOnAnyFiles(repoName, masterName);
        final int deletes = randomIntBetween(2, 10);
        final List<ActionFuture<AcknowledgedResponse>> deleteResponses = new ArrayList<>(deletes);
        for (int i = 0; i < deletes; ++i) {
            deleteResponses.add(client().admin().cluster().prepareDeleteSnapshot(repoName, "*").execute());
        }
        waitForBlock(masterName, repoName);
        awaitNDeletionsInProgress(1);
        for (ActionFuture<AcknowledgedResponse> deleteResponse : deleteResponses) {
            assertFalse(deleteResponse.isDone());
        }
        awaitNDeletionsInProgress(1);
        unblockNode(repoName, masterName);
        for (ActionFuture<AcknowledgedResponse> deleteResponse : deleteResponses) {
            assertAcked(deleteResponse.get());
        }
    }
    public void testMasterFailoverOnFinalizationLoop() throws Exception {
        internalCluster().startMasterOnlyNodes(3);
        final String dataNode = internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-test");
        final NetworkDisruption networkDisruption = isolateMasterDisruption(NetworkDisruption.DISCONNECT);