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
);
        PlainActionFuture.<RepositoryData, Exception>get(
            f -> repo.finalizeSnapshot(
                new FinalizeSnapshotContext(
                    ShardGenerations.EMPTY,
                    getRepositoryData(repoName).getGenId(),
                    state.metadata(),
                    snapshotInfo,
                    SnapshotsService.OLD_SNAPSHOT_FORMAT,
                    f,
                    info -> {}
                )
            )
        );
    }
    protected void awaitNDeletionsInProgress(int count) throws Exception {
        logger.info("--> wait for [{}] deletions to show up in the cluster state", count);
        awaitClusterState(
            state -> state.custom(SnapshotDeletionsInProgress.TYPE, SnapshotDeletionsInProgress.EMPTY).getEntries().size() == count
        );
    }
    protected void awaitNoMoreRunningOperations() throws Exception {
        awaitNoMoreRunningOperations(internalCluster().getMasterName());
    }
    protected void awaitNoMoreRunningOperations(String viaNode) throws Exception {
        logger.info("--> verify no more operations in the cluster state");
        awaitClusterState(
            logger,
            viaNode,
            state -> state.custom(SnapshotsInProgress.TYPE, SnapshotsInProgress.EMPTY).isEmpty()