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
createIndex("test-idx-1", "test-idx-2");
        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("test-idx-*")
            .get();
        assertThat(createSnapshotResponse.getSnapshotInfo().successfulShards(), greaterThan(0));
        assertThat(
            createSnapshotResponse.getSnapshotInfo().successfulShards(),
            equalTo(createSnapshotResponse.getSnapshotInfo().totalShards())
        );
        logger.info("--> truncate snapshot file to make it unreadable");
        Path snapshotPath = repo.resolve("snap-" + createSnapshotResponse.getSnapshotInfo().snapshotId().getUUID() + ".dat");
        try (SeekableByteChannel outChan = Files.newByteChannel(snapshotPath, StandardOpenOption.WRITE)) {
            outChan.truncate(randomInt(10));
        }
        startDeleteSnapshot("test-repo", "test-snap-1").get();
        logger.info("--> make sure snapshot doesn't exist");
        expectThrows(
            SnapshotMissingException.class,
            () -> client.admin().cluster().prepareGetSnapshots("test-repo").addSnapshots("test-snap-1").get().getSnapshots()
        );