best way to do this is cancel the original ticket, deposit those funds to your wallet, then you'll end up with all the money consolidated in your wallet and can reissue the new ticket. since you are gold/75K there are no cancel fees and this costs nothing to do except for some extra clicking. i do it all the time. AS is also pretty flexible in that if you want to retain part of the trip you can easily do that with the 'change flights' link, canceling off segments, redepositing those $$ into wallet, and then rebooking the new segments you need.