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.
test/framework/src/main/java/org/elasticsearch/snapshots/AbstractSnapshotIntegTestCase.java
}
    protected ActionFuture<AcknowledgedResponse> startDeleteSnapshot(String repoName, String snapshotName) {
        logger.info("--> deleting snapshot [{}] from repo [{}]", snapshotName, repoName);
        return clusterAdmin().prepareDeleteSnapshot(repoName, snapshotName).execute();
    }
    protected ActionFuture<AcknowledgedResponse> startDeleteSnapshots(String repoName, List<String> snapshotNames, String viaNode) {
        logger.info("--> deleting snapshots {} from repo [{}]", snapshotNames, repoName);
        return client(viaNode).admin().cluster().prepareDeleteSnapshot(repoName, snapshotNames.toArray(Strings.EMPTY_ARRAY)).execute();
    }
    protected static void updateClusterState(final Function<ClusterState, ClusterState> updater) throws Exception {
        final PlainActionFuture<Void> future = PlainActionFuture.newFuture();
        final ClusterService clusterService = internalCluster().getCurrentMasterNodeInstance(ClusterService.class);
        clusterService.submitUnbatchedStateUpdateTask("test", new ClusterStateUpdateTask() {
            @Override
            public ClusterState execute(ClusterState currentState) {
                return updater.apply(currentState);
            }
            @Override
            public void onFailure(Exception e) {
                future.onFailure(e);
            }
            @Override
            public void clusterStateProcessed(ClusterState oldState, ClusterState newState) {
                future.onResponse(null);
            }
        });
        future.get();
    }
    protected SnapshotInfo getSnapshot(String repository, String snapshot) {
        final List<SnapshotInfo> snapshotInfos = clusterAdmin().prepareGetSnapshots(repository).setSnapshots(snapshot).get().getSnapshots();