Search isn't working for me unfortunately, so here goes:

When last checking in at the Chicken around 6 months ago (my flying goes in spurts), I think the machine asked me what upgrade instrument I wanted to use, regional certs or 500-milers. This although I'd already indicated my choice soon after making the reservation.

Is it possible to confirm an upgrade with CR-1s or miles, then switch to 500-milers on checkin or before? It seems clear that this is do-able before the 100-hour mark (1Ks), how about after, and especially at check-in?

Thanks.