So assuming American release max of two F award seats on LAX-JFK and no more no matter what, and you are already booked on them, there will never be any further availability.

so if you are going SFO-LAX-JFK, all on an F award, you’ll never be able to change the first leg if a better connection opens up because there’s no availability in the second.

And what is the basis for your assertion that this is how AA will implement this.