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
private final DeleteRepositoryRequest request;
        UnregisterRepositoryTask(final DeleteRepositoryRequest request, final ActionListener<AcknowledgedResponse> listener) {
            super(request, listener);
            this.request = request;
        }
        /**
         * Constructor used by {@link org.elasticsearch.action.admin.cluster.repositories.reservedstate.ReservedRepositoryAction}
         * @param name the repository name
         */
        public UnregisterRepositoryTask(String name) {
            this(new DeleteRepositoryRequest(name), null);
        }
        @Override
        public ClusterState execute(ClusterState currentState) {
            Metadata metadata = currentState.metadata();
            Metadata.Builder mdBuilder = Metadata.builder(currentState.metadata());
            RepositoriesMetadata repositories = metadata.custom(RepositoriesMetadata.TYPE, RepositoriesMetadata.EMPTY);
            if (repositories.repositories().size() > 0) {
                List<RepositoryMetadata> repositoriesMetadata = new ArrayList<>(repositories.repositories().size());
                boolean changed = false;
                for (RepositoryMetadata repositoryMetadata : repositories.repositories()) {
                    if (Regex.simpleMatch(request.name(), repositoryMetadata.name())) {
                        ensureRepositoryNotInUse(currentState, repositoryMetadata.name());
                        ensureNoSearchableSnapshotsIndicesInUse(currentState, repositoryMetadata);
                        deletedRepositories.add(repositoryMetadata.name());
                        changed = true;
                    } else {
                        repositoriesMetadata.add(repositoryMetadata);
                    }
                }