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
protected boolean found = false;
        protected boolean changed = false;
        private final PutRepositoryRequest request;
        private final RepositoriesService repositoriesService;
        RegisterRepositoryTask(
            final RepositoriesService repositoriesService,
            final PutRepositoryRequest request,
            final StepListener<AcknowledgedResponse> acknowledgementStep
        ) {
            super(request, acknowledgementStep);
            this.repositoriesService = repositoriesService;
            this.request = request;
        }
        /**
         * Constructor used by {@link org.elasticsearch.action.admin.cluster.repositories.reservedstate.ReservedRepositoryAction}
         * @param repositoriesService
         * @param request
         */
        public RegisterRepositoryTask(final RepositoriesService repositoriesService, final PutRepositoryRequest request) {
            this(repositoriesService, request, null);