irods: no tools to update/overwrite a checksum in iRODS?

Apologies if I’m mis-reading a man page, or Doing This The Wrong way, but I can’t see a way to update the checksum of an object in iRODS.

As we are cleaning up some our our files in iRODS, we have found a few edge cases where;

1. a file is marked as zero length in iRODS with a checksum, but actually exists on disk with the path specified in the output of ils -L for the replica number
2. a file has a replica with a checksum that is right for all the other replicas, but wrong for this one. We want to preserve the file, so mark it as a dirty copy. To do this we need to update the checksum for that replica within iRODS, without making it the only good copy, so that iget will not retrieve it unless directed to the replica number manually.

Any suggestions? What have I missed?

Thanks,

John