Types of Colonization

Unfortunately, I don't think you can do this.

Space Empires Depot | SE:V Balance Mod

Too bad, two levels of each colonization tech would have been great... and only starting with breathable colony tech for your home planet type would be a challenge.

You can set up the game to be only colonizing breathable planets. but this is at startup and it's for the whole game.

SEV, more than a feeling.

Couldn't you set up the planet type data file with three more types, one for each breathable colonization type, then in systemType data file, put your three new types into the random selection code and edit each entry to account for the three new planet types?

Then for every system chance generated it will now have six planet types to choose from?

With the added colonization planet types, edit your component and tech tree accordingly. I would assume domed would be harder to research and implement than a planet with a suitable atmosphere.