Hi
Agent description is stored in servers table of database.
You may be able to update agent records massively, but it is not supported way.
If you want to do that, please take system backup before.
I tried following steps using RA 6.5 in house.
1. Stop RA service on management server.
2. Run following query.
update servers set server_description='BBB' where server_description='AAA'
3. Start RA service.
4. Open Automation Studio. Description was updated from AAA to BBB.
Thanks
Yas