And believe me, editing the overworld is really easy once you get the hang of it.
It actually is really easy, I was confused too, but when I went onto the Overworld Editor, I made my won overworld very easily, I just have to get the 'path' events down, then I can make a very awesome hack.
Anyways,
Go here,
youtube.com/chainfire9001
go to his videos then search "Overworld"
there are 7 parts to watch, I think you'll find making an overworld easier