Yes you can update the sysdevices table which is not a reccomended practice. However it's almost as easy to write a query against sysdevices to build a query to drop/add your backup devices as well. But is you want to execute against the system tables, here's a worthwhile reference to have on your desktop:
http://www.microsoft.com/sql/techinfo/productdoc/2000/systables.mspx
Also, in SQL 2K5 direct updates to the system tables are supposed go away.
RegardsRudy KomacsarSenior Database Administrator"Ave Caesar! - Morituri te salutamus."