Originally Posted by alexj7

Just want to list my experience with making a change in case this helps anyone.

-Booked A/J class from DAD-JFK round trip.
-I'm using this for actual vacation, but based in NYC. I'm actually out of vacation days for 2019 now with the first Vietnam trip due to other previously planned vacations. I would ideally change my return legs to 2020 so I can use it for a second real trip.
-Outbound from Vietnam is in a few weeks.
-Booked via priceline
-ITA matrix shows A/J availability without a stopover, however only right at the end of schedule (literally the last day or two on the calendar). This doesn't show up on Cathay Pacific website, and priceline could not see those dates yet, not surprisingly.
-A/J availability is pretty decent, as long as you take a >24h stopover in HKG. The fare allows this to occur without a reprice, but only on the inbound. My fare receipt doesn't list this, however, as it makes no mentions of stopovers in the rules.
-I called priceline and they could see the space to rebook in 2020 in A/J with a stopover in HKG. However, the repricing computer would only let the agent select out to Dec 25, 2019. They recommended I call CX directly.

I tried CX direct, but as I expected they can't modify it until I fly the first leg. At this point I can wait until I fly the first leg, then try the change via CX direct. Otherwise, I might wait a few days and try Priceline again to see if they can choose a later date.