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
.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("--> delete global state metadata");
        Path metadata = repo.resolve("meta-" + createSnapshotResponse.getSnapshotInfo().snapshotId().getUUID() + ".dat");
        Files.delete(metadata);
        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()
        );
    }
    public void testDeleteSnapshotWithCorruptedSnapshotFile() throws Exception {
        Client client = client();
        Path repo = randomRepoPath();
        createRepository(
            "test-repo",
            "fs",
            Settings.builder()
                .put("location", repo)
                .put("compress", false)
                .put("chunk_size", randomIntBetween(100, 1000), ByteSizeUnit.BYTES)
        );