RENAME a maintainer

>Alternatively, can I select all the objects with MNT-BY=<something> ??

  whois -ri mnt-by <your-mnt-obj-name-here>

>How can I change the MNT-BY attribute? Delete, and set up the new one? 

  I'd register the new one, move the objects under the control of the
  new one, double-check, and then delete the old one.

  Regards,
  Wilfried.