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.
test/framework/src/main/java/org/elasticsearch/snapshots/AbstractSnapshotIntegTestCase.java
Strings.toString(snapshotInfo, ChecksumBlobStoreFormat.SNAPSHOT_ONLY_FORMAT_PARAMS)
                    .replace(String.valueOf(Version.CURRENT.id), String.valueOf(version.id))
            )
        );
        final BlobStoreRepository blobStoreRepository = getRepositoryOnMaster(repoName);
        PlainActionFuture.get(
            f -> blobStoreRepository.threadPool()
                .generic()
                .execute(
                    ActionRunnable.run(
                        f,
                        () -> BlobStoreRepository.SNAPSHOT_FORMAT.write(
                            downgradedSnapshotInfo,
                            blobStoreRepository.blobStore().blobContainer(blobStoreRepository.basePath()),
                            snapshotInfo.snapshotId().getUUID(),
                            randomBoolean()
                        )
                    )
                )
        );
        final RepositoryMetadata repoMetadata = blobStoreRepository.getMetadata();
        if (BlobStoreRepository.CACHE_REPOSITORY_DATA.get(repoMetadata.settings())) {
            logger.info("--> recreating repository to clear caches");
            assertAcked(client().admin().cluster().prepareDeleteRepository(repoName));
            createRepository(repoName, repoMetadata.type(), Settings.builder().put(repoMetadata.settings()));
        }
        return oldVersionSnapshot;
    }
    protected SnapshotInfo createFullSnapshot(String repoName, String snapshotName) {
        return createFullSnapshot(logger, repoName, snapshotName);