Is it possible to change the tree types present in a world manually?

[neal_]

As the title suggests, I want to change which trees I have in my world. I have all the classic ones and they kind of bore me. Is there any way to do this without breaking the world?
I found this on reddit, it explains it a bit more: http://www.reddit.com/r/Terraria/comments/1u54cu/different_types_of_trees/

 

[darthmorf]

There's a program isn't there? Or is that just for generating worlds...?