to the first question: You can create a new line in the items file in the scripts folder of dragon. Then you make a new txt (like grass_empty.txt) without any items in it (not sure if this works though, I never tried it). Then you give in the coordinates like the syntax says:
[SourceGroup] [ChanceToPlace] [Left] [Top] [Right] [Bottom] [Filename]
The left/top/right/bottom would be the field it applies to. I'm not sure what to give in for the SourceGroup (But I'm sure others here would know :p).
Disclaimer: I'm not sure if this works. I've never tried it myself.
