I never broke the Galactic Code. I think it has to do with destroying a planet with a Planet Buster. Is there any other way to do that? I never even saw the words "Galactic Code" pronounced in the game.
Terraforming a T0 planet is the same as terraforming any other planet. Just heat it up, cool it down, add atmosphere, remove atmosphere as needed. You see that in the rings at the bottom left of your screen. When the ring turns orange. It's time to add a small plant, a medium plant and a large plant. Do it quickly but you do have some time. Have them in your cargo. That stabilizes the planet. Then you're free to add two herbivores and a carnivore/omnivore. I dunno, it's rather simple I don't know what's so different from terraforming any other planet from any score to another.