if the chtonian transformation reduces the size of a planet, what happens to the structures if they exceed the size limit? so like 69 space filled up, then the space is only 57, do the structures dissappear or is it like 69/57 size used up?

They should go offline; any structures past the size of the planet will stop giving their bonus. The structures will stop working from the bottom of the list up, until the working structures take up less than or equal to the planet's size.

Can only be used on an unoccupied planet.

-_- Oh yeah, didn't think about that.

so where were you getting your information from? sounded like on-the-spot waffle to me haha, correct me if im wrong and theres any examples of such thing

and unoccupied eh, didnt notice that part either lol

Yes, there have been examples, but mostly regarding exploits. There isn't anything that would officially cause that affect anymore.