You are simply not getting it. I have a PAPER TICKET. The issue is not changing the reservation, it is presenting an OPEN (PAPER) ticket coupon at CHECK IN to BA or CX or whatever (non-AA) airline that segment is booked on. I'm not always able to get to an AA ticketing outlet to get a new ticket coupon printed before I check in, and frankly I don't want that hassle anyway.

Even before e-tickets became "mandatory" I used to get hassle from a few places who insisted that they take the ticket off to their airport ticketing office to get a paper sticker put on it. Now I fear that they will want to charge me at check-in for revalidating a perfectly valid PAPER ticket coupon.