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(createSnapshotResponse.getSnapshotInfo().successfulShards(), greaterThan(0));
        assertThat(
            createSnapshotResponse.getSnapshotInfo().successfulShards(),
            equalTo(createSnapshotResponse.getSnapshotInfo().totalShards())
        );
        logger.info("--> move index-N blob to next generation");
        final RepositoryData repositoryData = getRepositoryData(repoName);
        Files.move(repo.resolve("index-" + repositoryData.getGenId()), repo.resolve("index-" + (repositoryData.getGenId() + 1)));
        assertRepositoryBlocked(client, repoName, snapshot);
        if (randomBoolean()) {
            logger.info("--> move index-N blob back to initial generation");
            Files.move(repo.resolve("index-" + (repositoryData.getGenId() + 1)), repo.resolve("index-" + repositoryData.getGenId()));
            logger.info("--> verify repository remains blocked");
            assertRepositoryBlocked(client, repoName, snapshot);
        }
        logger.info("--> remove repository");
        assertAcked(client.admin().cluster().prepareDeleteRepository(repoName));
        logger.info("--> recreate repository");
        assertAcked(
            client.admin()
                .cluster()
                .preparePutRepository(repoName)
                .setType("fs")
                .setSettings(
                    Settings.builder()
                        .put("location", repo)
                        .put("compress", false)
                        .put("chunk_size", randomIntBetween(100, 1000), ByteSizeUnit.BYTES)
                )
        );