It is only possible to copy a whole building.
However, I heard if you copy a TC that has another building covering a part of it and remove that other building during the game, it will get rid of the part the building was on. I will look for some past posts.
Post 1Post 2Only ones I could find. [This message has been edited by Aro (edited 01-19-2003 @ 07:30 PM).]