I'm going to make a bc iced cake and let it crust then i was going to press with a mat. My question is i want to trace some of the impressed parts what do i use is bc ok on top of crusted bc of or is it going to fall off? any help thanks ! you guys are awsome!!

piping buttercream onto crusted buttercream should work fine.

you shouldn't have any problems, just like JoAnnB said, should work fine.
Allee

Thanks