Mate, using AA miles means you should be over in the AA forum.

If you end up using Asia Miles....which it doesn't sound like....you can only upgrade Y,B,H,K, and M subclass economy tix to PEY.

No currency except CX's Asia Miles can be used for upgrades.

And no you can't swap seats midflight. Although I hear it happens sometimes....I guess it comes down to the ISM. But the straightforward answer is "no".