For locations, you can do it through the GUI via Manage->Assets. Locations are found under organizational types. This does preserve the GUID just fine. That said, if you really desperately want to change it via SQL, the location name is stored in the name field in the dbo.Item table. Needless to say, changing it there isn't supported by Symantec, I'd think.
Regarding departments, the thing to question is whether or not you import departments from AD. My environment does, which means all I need to do is rename a department in AD and it will sync up with ITMS. Additionally, you can create new departments and rename existing ones just like locations from Manage->Assets. If you are importing from AD though, I'm pretty sure the next sync will rename any existing ones back to what they are in AD. Again, if you really want to change it via SQL, I think the dbo.RM_ResourceDepartment table holds what you want.
I suppose I should point out that both those table names only hold the name field. If you are looking for additional details, you'll want to chase those details tables down. The easiest way to do that, IMHO, is to view the design of the location and department views in the DB. You may have ot go back a couple levels, but you should be able to find them.