Ideas:
You design the blueprint for a ship, then you use it to create the ship. Can't create blueprint from the ship. Can't edit "bought" ships.
Can buy, say, a core unit that supplies a blueprint around it, once built, it reverts to a normal core unit (blueprint lost).
This ship, built by you, off someone else's blueprint, can be edited by you, and on-sold (if desired), but you are unable to create a blueprint for this new ship unless you do it from scratch.
That way, "normal-quality" ships can be supplied as blueprint core units, that people can build and after that, edit. (must be built EXACTLY to the blueprint before it can be edited). If people go to the effort of reverse engineering, good for them, but not worth it.
Higher-quality ships sold as pre-built, and those ships can't be edited unless you take them back to the creator, and request the changes.