Originally Posted by JohnAx
In my experience only the issuing carrier has access to your PNR so the others aren't willing/able to make changes to your tickets, or even change reservations on themselves. They always want you to call the issuing carrier. Once I asked CX to waitlist an A segment with a D backup against a BA-issued OWE. Being their gracious selves they did it by creating their own pnr for that segment, and made me give them the ticket number so they could hold the space.
I had no problems in getting the AA desk at LHR to change reservations on a BA AONE3 issued in CAI, this was for AA and CX sectors a couple of months ago.