If you're changing airlines, AA charges a fee:
"For awards involving travel on other airlines, origin or destination changes or changes to the airline(s) in the itinerary will incur a change fee of $150, even when retaining the same award type"
https://www.aa.com/i18n/AAdvantage/r...false&from=Nav
If you do book QR flights, if J opens up later, AA should change it without a fee.
Oh, and CX via HKG ain't gonna happen AA requires transatlantic to HYD (but you can fly YVR-JFK on CX then on to HYD)