I've been experimenting with adding buffs to custom CAS parts, and it doesn't seem to be working. I noticed there was a field in the CASP file called "BuffResKey" which points to a buff file, and "TGI...
Just verified this working on the latest patch 1.2.24.20. Attached is the test package I created, it adds an angry buff to the Darth Vader helmet (which seemed appropriate).