I wouldn't count on that. It will be a challenge to find a QR agent able and willing to make such changes. Also I don't think QR will make voluntary changes to a ticket issued by AA (or any other airline for that matter).
My experience has been that both points are the case. There was a time when most OneWorld airlines were willing to take over and make changes to an RTW ticket issued by another, and QR used to have competent agents familiar with RTWs available. My experience has been that neither has been the case for some time now.