I'm making major changes to the techtree in my mod, for one, I am adding a Colossus sized hull. Basically it's twice as big as Massive. I disliked how with the Massive hulls, at end game they only take 30 or so turns to churn out, but when you have 30 or so planets, you're basically making them 1 per turn. So I've added a new plantary improvement called Colossus Ship Yard. It's a super project, so you can only have 1. And I want Colossus Hulls to require it for a prerequisite. In other words, you can only build Colossus ships on that planet.

However, I can't figure out how to add that planetary improvement as a prerequisite for the Colossus Hull and be planet specific. So that you can't build it anywhere else.

Is this even possible?