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
client().admin()
                .cluster()
                .prepareCreateSnapshot(repoName, "fast-snapshot")
                .setIndices(indexFast)
                .setWaitForCompletion(true)
                .execute()
        );
        assertThat(createSlowFuture.isDone(), is(false));
        unblockNode(repoName, dataNode);
        assertSuccessful(createSlowFuture);
    }
    public void testDeletesAreBatched() throws Exception {
        internalCluster().startMasterOnlyNode();
        final String dataNode = internalCluster().startDataOnlyNode();
        final String repoName = "test-repo";
        createRepository(repoName, "mock");
        createIndex("foo");
        ensureGreen();
        final int numSnapshots = randomIntBetween(1, 4);
        final Collection<String> snapshotNames = createNSnapshots(repoName, numSnapshots);
        createIndexWithContent("index-slow");
        final ActionFuture<CreateSnapshotResponse> createSlowFuture = startFullSnapshotBlockedOnDataNode(
            "blocked-snapshot",
            repoName,
            dataNode
        );
        final Collection<StepListener<AcknowledgedResponse>> deleteFutures = new ArrayList<>();
        while (snapshotNames.isEmpty() == false) {
            final Collection<String> toDelete = randomSubsetOf(snapshotNames);
            if (toDelete.isEmpty()) {