*Raises an accusing finger in the general direction of Renegade, and hits Ctrl-D* Don't worry; mistakes happen, and it is always nice to have some material for blackmails.
To the best of my knowledge, you cannot change the type of a planet through Stellar Manipulation, but only its atmosphere. At least, I have been unable to transform Rock planets into something else in NGC5 (after a couple of tries). Either I have been unlucky, or it cannot be done.