Changing the board image when adding extension

I decided to step up and work on getting a Firefly The Board Game module going in Vassal, and I’m running into an issue when I try adding in expansions. I created a base module, loaded in the base game map, and it opens fine.

Once I start working on Blue Sun and Kalidasa, I need it to add those board areas to the main map. My question is, is it possible to have an extension change what board image is loaded, or do I have to have the expansion load just the added part of the game and somehow tell it where to place it in relation to the main map?

I’m just starting out with all this, so if you can give me a step by step on how to do this, I would appreciate it. I know there is a way to have extra boards load in a new window (like how the Battlestar Galactica module does it), but I’d really like to be able to have it load right next to the main board in the main window as that’s how it works in the actual game.