Depends on cabin load, if one is lucky enough to have an empty cabin or just one other fellow passenger, I would gladly trade the 2A to the D/K side, with one seat for watching TV one seat for sleeping.
That said, calling HK and just pick the option of already having a booking, ignore the phone menu, would get the human agent who would assign 1A or 2A if not already taken.
OWR does not get privilege in KA's seat assignment in my experience.
I dont really like to change the AS FF number to AA FF number because once you do that, the reservation would drop off from AS site I guess you could still pull it up by AS PNR, but that is a hassle. I prefer to be able to see it when I get to AS site. This way, if there is any schedule changes, not just the CX segment, but also the AS segment, I can see the warning right away. I generally only do this very close to departure time. But in recent years I dont bother to do so any more. Just called CX to get the seats. Or some mentioned twitter worked also.
Also it seems once you change the FFP number, you cannot change it back - at least that was the experiences using QR / AY sites to do it on BA issued tickets. This is particularly annoying when it comes the need to cancel a BA award. Had to dig up BA PNR to make the reservation showed up so I could cancel it.