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
Collections.emptyMap(),
            ShardGenerations.EMPTY,
            IndexMetaDataGenerations.EMPTY,
            RepositoryData.MISSING_UUID
        ); 
        Files.write(
            repo.resolve(BlobStoreRepository.INDEX_FILE_PREFIX + withoutVersions.getGenId()),
            BytesReference.toBytes(
                BytesReference.bytes(withoutVersions.snapshotsToXContent(XContentFactory.jsonBuilder(), Version.CURRENT, true))
            ),
            StandardOpenOption.TRUNCATE_EXISTING
        );
        logger.info("--> verify that repo is assumed in old metadata format");
        final ThreadPool threadPool = internalCluster().getCurrentMasterNodeInstance(ThreadPool.class);
        assertThat(
            PlainActionFuture.get(
                f -> threadPool.generic()
                    .execute(
                        ActionRunnable.supply(
                            f,
                            () -> SnapshotsService.minCompatibleVersion(Version.CURRENT, getRepositoryData(repoName), null)
                        )
                    )
            ),
            is(SnapshotsService.OLD_SNAPSHOT_FORMAT)
        );
        logger.info("--> verify that snapshot with missing root level metadata can be deleted");
        assertAcked(startDeleteSnapshot(repoName, snapshotToCorrupt.getName()).get());
        logger.info("--> verify that repository is assumed in new metadata format after removing corrupted snapshot");
        assertThat(