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
Files.delete(
                    shardZero.resolve("index-" + getRepositoryData("test-repo").shardGenerations().getShardGen(indexIds.get(index), 0))
                );
            }
            Files.delete(shardZero.resolve("snap-" + snapshotInfo.snapshotId().getUUID() + ".dat"));
        }
        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()
        );
        for (String index : indices) {
            assertTrue(Files.notExists(indicesPath.resolve(indexIds.get(index).getId())));
        }
    }
    public void testDeleteSnapshotWithMissingMetadata() throws Exception {
        Client client = client();
        Path repo = randomRepoPath();
        createRepository("test-repo", "fs", repo);
        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()