I now see what you trying to address !
Due to multiple trigger scenario introduced in the later versions ( to allow homegrown triggers on tables in vended/third party applications e.g.) the loginame in sysobjects has become exclusive owner of trigger logic in a way.
pre-ASE 15, I have used the path you suggested ( to update sysobjects.loginame ) for dropping a user who was no longer around but owned objects. May be you can use that as a last resort till SAP/Sybase comes up with a solution / work around.
If they stick to their guns then you have to drop/create the trigger in one single DDL transaction.
HTH
Avinash