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/main/java/org/elasticsearch/repositories/RepositoriesService.java
import org.elasticsearch.cluster.ClusterChangedEvent;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.ClusterStateApplier;
import org.elasticsearch.cluster.ClusterStateUpdateTask;
import org.elasticsearch.cluster.RepositoryCleanupInProgress;
import org.elasticsearch.cluster.RestoreInProgress;
import org.elasticsearch.cluster.SnapshotDeletionsInProgress;
import org.elasticsearch.cluster.SnapshotsInProgress;
import org.elasticsearch.cluster.metadata.IndexMetadata;
import org.elasticsearch.cluster.metadata.Metadata;
import org.elasticsearch.cluster.metadata.RepositoriesMetadata;
import org.elasticsearch.cluster.metadata.RepositoryMetadata;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.node.DiscoveryNodeRole;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.component.AbstractLifecycleComponent;
import org.elasticsearch.common.regex.Regex;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.util.concurrent.ConcurrentCollections;
import org.elasticsearch.core.IOUtils;
import org.elasticsearch.core.SuppressForbidden;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.Index;
import org.elasticsearch.repositories.blobstore.MeteredBlobStoreRepository;
import org.elasticsearch.snapshots.Snapshot;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.TransportService;
import java.io.IOException;