I am wondering if the ticket number starts with CX or AS( each airline has specific airline number). If I contact AS for the change, I can not stand by since it is the partner airline. If I call CX, they should be able to track the reservation. They can do the waitlist or standby for me. The thing is: is CA able to see the reservation is done by AS? If yes, will they be leaving the responsibility to AS? Can they do the change anyway?