Certain levels of terraforming via magic have occurred. In the Forgotten Realms you get some of that with Netheril and some others I think. I found it acceptable if the story works for that. Celestial dynamics? Well, then it seems like you're gonna have to get some deities involved and that seems like it REALLY needs a GOOD story to make it believable. Or just to reason out why it would happen in the first place.
That being said, the right story can tell just about any tale.