I know i sound like a complete idiot, but how do you do that...? sorry for my lack of know how!
In OBMM, go to utilities-->Archive Invalidation->Reset BSA Timestamps
Edit: There are many, many users (of OBMM) who do not know about that function. Really, it is nothing bother yourself about. I have not used a cosmetic mod with files packaged in a BSA, hmmm... If you repacked the Vanilla BSAs...Well, good luck!