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
awaitNumberOfSnapshotsInProgress(3);
        unblockNode(repository, master);
        assertAcked(deleteFuture.get());
        assertAcked(cloneFuture.get());
        awaitNoMoreRunningOperations();
        assertThat(snapshot1.get().getSnapshotInfo().state(), is(SnapshotState.PARTIAL));
        assertThat(snapshot2.get().getSnapshotInfo().state(), is(SnapshotState.PARTIAL));
    }
    public void testQueuedSnapshotAfterPartialWithIndexRecreate() throws Exception {
        internalCluster().startNodes(3);
        
        
        final Settings highShardCountSettings = indexSettingsNoReplicas(randomIntBetween(12, 24)).build();
        final String index1 = "index-1";
        createIndexWithContent(index1, highShardCountSettings);
        final String index2 = "index-2";
        createIndexWithContent(index2);
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        final ActionFuture<CreateSnapshotResponse> partialFuture = startFullSnapshot(repoName, "partial-snapshot", true);
        blockAllDataNodes(repoName);
        waitForBlockOnAnyDataNode(repoName);
        
        
        assertAcked(client().admin().indices().prepareDelete(index1).get());
        createIndexWithContent(index1, highShardCountSettings);
        final ActionFuture<CreateSnapshotResponse> nonPartialFuture = startFullSnapshot(repoName, "full-snapshot");
        unblockAllDataNodes(repoName);
        assertSuccessful(nonPartialFuture);
        assertSuccessful(partialFuture);