Woo! A day of updates! I've made a few updates to this tool, so hopefully you'll find them useful:
2018-08-12: A reader noticed that the UpdateAdminSDHolder switch didn't work ask expected when specifying the ExchangeHybridWriteBack OU without the ExchangeHybridWriteBackOUs parameter. I have found and updated that! Thanks, Mark!
2018-06-03: A large customer asked if I could put a parameter in to skip delegating writeback permissions to InetOrgPerson objects. Asked and answered!
As always, the updated version is available at http://aka.ms/aadpermissions. Happy delegating!