Update for my fellow FTers. I was able to successfully change my ticket.
This is for fare basis AAARRVN8 which booked into A/J. I booked via Priceline. Calling them was useless as they always quoted a really high $ figure, even for flights with clear A/J availability. I flew the outbound already, so that opened up calling CX directly for changes instead. Preparing for the worst, I just called, and the change was actually super easy - probably thanks to advanced research into the issue. I made sure to feed the agent flights with definite A/J availability. Note, I was only able to get that by forcing a stopover in HKG, which I am fine with.
What I did was search using ITA matrix like this:
I was looking for late 2019 or early 2020. Late 2019 was basically non-existent. I was worried about booking into 2020, since some reported that ticket validity is one year from
purchase, although my receipt didn't mention that, just one year from travel commencement and also something about only until Jan 31 2020. I decided to try a date in early January first, and that worked. Only owed the $100 change fee per passenger, plus a minor tax for HKG of about ~$10-20 (too excited at that point to care
)
So basically, if you want to reschedule just the return flight, you may have luck in early 2020. There were also some dates from now until October open, but Nov/Dec were completely unavailable.