We're moving our Directory Services from OD to AD, so all of our user and group uniqueIDs and GeneratedUIDs will be changing. However, wanted to keep the POSIX owner/group and ACLs on our file system. When setting up Active Directory in Directory Services you can map UID, primaryGroupID, and groupId to other AD attributes, but it doesn't help with ACLs (which use the GeneratedUIDs) and it means you have to manually manage those mapped attributes after the migration.
So, I created a script to migrate a file system from one directory service to another. Here it is if you ever find yourself dealing with this.