We've been talking about standy at the airport immediately prior to the flight (at most 2 hours before); whole different process when not at the airport, and not standby. CX cannot reissue AA award tickets, it is controlled and locked by AA (their decision). So you must phone AA or go to an AA ticket office; CX can never help with this (though they often will phone AA for you under the covers, so maybe seems like CX made the change). Your disappointment is with AA and not CX, in this instance.