Data point: I had 2 F seats on CX 898 HKG to LAX on a Wednesday. CX quit flying 898 on Wednesdays, and sort of booked us (but not ticketed) on the next flight to LAX (884) which has no F cabin (and bad layover times). I called AAdvantage and a Ticketing Supervisor (first Filipino agent had no clue) wrote up a request to the "CX liason" for 2 F seats on 882. I first requested 898 on Thursday with an overnight in HKG, but exceeding 24 hours in HKG would not be permitted by AA.

I received an email that the revised ticketing was complete within 18 hours even though they said it might take several days.