When I book a ticket to take advantage of the *A 55555 miles bonus, how should I deal with FF numbers? I'll fly 2 x 5 segments on different companies, so I plan to put half of them on AP and the other half on M&M.

Would it be safe to give my AP number when I book to get premium Y seats if possible, and then ask to change it to M&M when I check in? Or should I wait until I come back to mail the boarding passes?

It may be worth paying $2800 for 111110 miles, but certainly not for 55555 if somehow I couldn't credit 5 flights on M&M...