To answer my own question - just in case useful to someone … I flew the outbound, then called VA and was told if I went to the website to manage my reservation, from there I’d want to use the website chat function to connect to an agent to change the date of the flight. So before calling I identified a date next year when same flight was available at the same rate - supposedly you feed that info to the chat agent and they make the change. And of course later on you can call in again and actually change to a flight you actually want to take.

I can’t tell you that this works seamlessly or if any fees are charged because I ended up sticking with my original return flight.