I apologize if this question is a bit off-topic for the original thread, but the subject of switching FF numbers has come up and so now seems like the best time to ask this...

Is it possible to switch FF numbers on an award ticket? For instance, say that I want to redeem DL SkyMiles for an award ticket on CO (I guess for this example, assume both code and metal are CO). I book the ticket, and at this point I assume that my DL# is attached to the ticket. Is it possible to change after booking the FF# to my OnePass#? How about at check-in?