[fatboyslim]

I take it that when you say acrylic you mean the clear/lacquer top coat?
if this is the case then yes you can put the decals on first BUT test the lacquer fist on a decal that you won't use as some lacquers will ruin the decals.
Personally I've never used a lacquer I just give the painted body a good old polish (Autoglym-hell if it's good enough for Aston Martin then it'll do for my models) stick the decals on then give it a final buff (once the decals have dried) to remove any finger prints and thats it.

Anyway Welcome to A.F enjoy your stay and don't forget to check out the Modelling Forum F.A.Q page the information there would cost thousands but we dish it out for free!!