For V4, I suggest that any default images provided by Vassal be available for use (perhaps a new /default-img folder) in the module structure.
I’ve just implemented a “Normalized” d6 (rolls 3d6 and maps the result to 1-6) for less “swingy” results in a certain critical CRT.
I implemented this as a GKC and wanted to re-use the standard Vassal “die” symbol, but it is apparently hard coded into Vassal, rather than in the module images directory.