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
assertThat(client().admin().cluster().prepareGetSnapshots(repoName).get().getSnapshots(), empty());
    }
    public void testQueuedDeletesWithOverlap() throws Exception {
        final String masterNode = internalCluster().startMasterOnlyNode();
        internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-one");
        createNSnapshots(repoName, randomIntBetween(2, 5));
        final ActionFuture<AcknowledgedResponse> firstDeleteFuture = startAndBlockOnDeleteSnapshot(repoName, "*");
        final ActionFuture<CreateSnapshotResponse> snapshotFuture = startFullSnapshot(repoName, "snapshot-queued");
        awaitNumberOfSnapshotsInProgress(1);
        final ActionFuture<AcknowledgedResponse> secondDeleteFuture = startDeleteSnapshot(repoName, "*");
        awaitNDeletionsInProgress(2);
        unblockNode(repoName, masterNode);
        assertThat(firstDeleteFuture.get().isAcknowledged(), is(true));
        
        assertThat(secondDeleteFuture.get().isAcknowledged(), is(true));
        
        final SnapshotException snapshotException = expectThrows(SnapshotException.class, snapshotFuture::actionGet);
        assertThat(snapshotException.getMessage(), containsString(SnapshotsInProgress.ABORTED_FAILURE_TEXT));
        assertThat(client().admin().cluster().prepareGetSnapshots(repoName).get().getSnapshots(), empty());
    }
    public void testQueuedOperationsOnMasterRestart() throws Exception {
        internalCluster().startMasterOnlyNodes(3);
        internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndexWithContent("index-one");
        createNSnapshots(repoName, randomIntBetween(2, 5));