Got a doc off of EMC Powerlink.
1. On the NetWorker Server run the mminfo query below to get the client ID, and copy it in a safe place (the clientid is the second field of the output).
# mminfo -av -r client,clientid | sort | uniq
2. Delete the client resource for client "client".
3. Shutdown NetWorker services.
4. Rename /nsr/mm to /nsr/mm.old:
# mv /nsr/mm /nsr/mm.old
5. Restart the NetWorker services.
6. Create a client with new name (clientbk) and use the old client name's (client) client ID (the one that been supplied in the mminfo output in step 1), and make sure that the older client ID is specified in the "Globals 1 of 2" tab.
7. Shutdown NetWorker services again.
8. Check the /nsr/index directoy, and if you find an index folder with the new name (clientbk), rename it to any other name.
9. Rename /nsr/index/(client) to /nsr/index/(clientbk)
# mv /nsr/index/(old_client_name) /nsr/index/(new_client_name)
10. Remove the newly created /nsr/mm.
# rm -rf /nsr/mm
11. Rename /nsr/mm.old back to /nsr/mm
# mv /nsr/mm.old /nsr/mm
12. Start NetWorker services again and test a backup for the renamed client.