Hi all,
I created a small Java utility here: GitHub - delatbabel/vassal_extension_utility: Utility for moving things between vassal modules and extensions · GitHub to move objects between two extensions of a module, or between a module and an extension. I have successfully used it to search for objects in a module and move them to an extension so that’s a start. The idea being that it can be used to break up large modules into smaller modules with extensions – especially useful with large numbers of things like optional units extensions that don’t have to be loaded every game.
I haven’t sorted out the build and packaging stuff yet, so it’s just a Makefile to build and run the utility.
Anyone can grab the source files and have a play.