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 repository = "test-repo";
        createRepository(repository, "mock");
        final String sourceSnapshot = "source-snapshot";
        createFullSnapshot(repository, sourceSnapshot);
        final IndexId index1Id = getRepositoryData(repository).resolveIndexId(index1);
        blockMasterOnShardLevelSnapshotFile(repository, index1Id.getId());
        final String cloneTarget = "target-snapshot";
        final ActionFuture<AcknowledgedResponse> cloneSnapshot = clusterAdmin().prepareCloneSnapshot(
            repository,
            sourceSnapshot,
            cloneTarget
        ).setIndices(index1, index2).execute();
        awaitNumberOfSnapshotsInProgress(1);
        waitForBlock(master, repository);
        final ActionFuture<CreateSnapshotResponse> snapshot2 = clusterAdmin().prepareCreateSnapshot(repository, "snapshot-2")
            .setIndices(index2)
            .setWaitForCompletion(true)
            .execute();
        assertSuccessful(snapshot2);
        unblockNode(repository, master);
        assertAcked(cloneSnapshot.get());
        assertAcked(startDeleteSnapshot(repository, cloneTarget).get());
        assertThat(
            clusterAdmin().prepareSnapshotStatus().setSnapshots("snapshot-2").setRepository(repository).get().getSnapshots(),
            hasSize(1)
        );
    }
    public void testCorrectlyFinalizeOutOfOrderPartialFailures() throws Exception {
        internalCluster().startMasterOnlyNode();
        final String dataNode1 = internalCluster().startDataOnlyNode();