Originally Posted by
Calchas
It can be done, and indeed it should not incur a fee. I would ask another agent and press them for their reasons.
(The only reason it might not be possible is if availability differs in the codeshare and D class is zeroed out.)
Which, to confirm, you can look up in expert flyer (under AA).
I'd say no harm in calling AA and asking if they've do the change for you. Given you're switching a flight to them and it sounds like you are going over an ocean with them they may well be up for it without a charge as there's no re-routing.