You download a design form the workshop, it is saved as a design which you can use in game or use to create a ship style(if you have lots of designs). To change a designs hull size, you have to either create a shipstyle(out side of the game modding) and list the design you downloaded as a medium hull(The game will still think its a cargo hull due to the design). You then boot the game up, start a game, use the unlock command, find your ship pr ships, save it as a template, then re edit your shipstyle to point at this new template which is now saved as a medium hull or what hull type you chose in your ship style.
You have to create the XML's to do this. All of them. OR, edit existing xml's of which I listed above.
