Is it possible to extract the models in a module so that they can be edited? Or make your own custom models and put them in a finished module?
Not an expert (I just use the built-in module editor) so take the following with a grain of salt…
If you are referring to the images (‘models’?) then the answer is yes. You can extract the entire module using any application than unzip zip files. Then you can edit images and save them, but do not change file names or you will have edit the actual module using the VASSAL module editor (except for a few geniuses who edit the build file - not recommended if you do not know a lot about the inner workings of the module builder). Finally, you need to re-zip the stuff and then you have a new module. Of course, the person you are playing may not be able to read your game files if they do not have the same modification, but maybe?
VASSAL geeks - did I get something wrong here?