Question for everyone:

I want to book a milage run on CO.com flying CO. If I dont sign in using my OP#(I have no status on CO) and just use as a guest I can input my NW FF#. I am NWA Silver will the EUA run on non NWA code share CO flights. The flights on CO are mainline flight numbers. Will CO system catch my NWA FF# for the EUA??? or would I be stuck in Y??