On a DONE3 currently. Had first flight last week.
Wanting to change 2nd last flight ~4 weeks away. (HKG-SIN to a later flight)

Rules state this type of change is free, but I've had some push back on that while trying to do changes like this in recent years.

Who will asking about the change be easier? QF (ticket issuer), CX (operator) or AA (marketing carrier).