This working for everyone besides me?
I figured out why sometimes it works and others its grayed out on Finnair.
When booking the ticket, I used to remove my BA# which is automatically filled in.
If you leave it in there, you are able to make the switcheroo on Finnair.
Remove it when making the booking and you will have to call AA to add the # in (or use RJ.com and have all your passport info available)