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/CorruptedBlobStoreRepositoryIT.java
ensureGreen();
        logger.info("--> verify index-N blob is found at the new location");
        assertThat(getRepositoryData(repoName).getGenId(), is(beforeMoveGen + 1));
        startDeleteSnapshot(repoName, snapshot).get();
        logger.info("--> verify index-N blob is found at the expected location");
        assertThat(getRepositoryData(repoName).getGenId(), is(beforeMoveGen + 2));
        logger.info("--> make sure snapshot doesn't exist");
        expectThrows(
            SnapshotMissingException.class,
            () -> client().admin().cluster().prepareGetSnapshots(repoName).addSnapshots(snapshot).get()
        );
    }
    public void testHandlingMissingRootLevelSnapshotMetadata() throws Exception {
        Path repo = randomRepoPath();
        final String repoName = "test-repo";
        createRepository(
            repoName,
            "fs",
            Settings.builder()
                .put("location", repo)
                .put("compress", false)
                
                .put(BlobStoreRepository.CACHE_REPOSITORY_DATA.getKey(), false)
                .put("chunk_size", randomIntBetween(100, 1000), ByteSizeUnit.BYTES)
        );
        final String snapshotPrefix = "test-snap-";
        final int snapshots = randomIntBetween(1, 2);
        logger.info("--> creating [{}] snapshots", snapshots);
        for (int i = 0; i < snapshots; ++i) {