Does this mean there's actually 4 available on SFO-HKG-SIN?

I am originally booked on LAX-HKG-KUL-SIN because CX, because CX did not release any award seats on their HKG-SIN route for that date at all. This is on CX, Dragon Air, then Malaysia Air (in that order). If I change my routing to go from LAX-SFO-HKG-SIN which allows me to keep the origin and destination the same, but the carriers will now be AA, CX, will there be a change fee? I was told that it would be $150 per person because it's a different award. That person from AA was not helpful and didn't elaborate on why other than saying it's a different type of award.

Alternatively, I can wait till close to departure date and if HKG-SIN opens up, I can change on LAX-HKG-SIN all on CX. But this means I will drop Dragon Air and Malaysia Airlines. Will there be a change fee in this case? I saw on the AA website that they charge fees for changing carriers.