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
assertThat(snapshotInfo2.indices(), hasSize(1));
    }
    public void testDeleteSnapshotWithMissingIndexAndShardMetadata() throws Exception {
        Client client = client();
        Path repo = randomRepoPath();
        createRepository("test-repo", "fs", repo);
        final String[] indices = { "test-idx-1", "test-idx-2" };
        createIndex(indices);
        logger.info("--> indexing some data");
        indexRandom(
            true,
            client().prepareIndex("test-idx-1").setSource("foo", "bar"),
            client().prepareIndex("test-idx-2").setSource("foo", "bar")
        );
        logger.info("--> creating snapshot");
        CreateSnapshotResponse createSnapshotResponse = client.admin()
            .cluster()
            .prepareCreateSnapshot("test-repo", "test-snap-1")
            .setWaitForCompletion(true)
            .setIndices(indices)
            .get();
        final SnapshotInfo snapshotInfo = createSnapshotResponse.getSnapshotInfo();
        assertThat(snapshotInfo.successfulShards(), greaterThan(0));
        assertThat(snapshotInfo.successfulShards(), equalTo(snapshotInfo.totalShards()));
        final Map<String, IndexId> indexIds = getRepositoryData("test-repo").getIndices();
        final Path indicesPath = repo.resolve("indices");
        logger.info("--> delete index metadata and shard metadata");
        for (String index : indices) {
            Path shardZero = indicesPath.resolve(indexIds.get(index).getId()).resolve("0");
            if (randomBoolean()) {