Hi, yes, you need to make a mod (no coding required, just editing .json config files; example, docs and references in Mods folder), save your desired ship with f6, copy paste the new ship from Ships folder in the mod molder and give it the same identifier as the current one one to overwrite it.
or the simpler way, save your design (f6), enable creative at start(F1), destroy your ship (enable god mode so you would not die with F2, type /destroyship in chat), and spawn the new one(F3 -> left ship list click spawn), but creative prevents registering finished games on the leaderboard