Because the tile sets may not be the same for each land level the only change that will really work with any amount of success is from Plains, Swamp or Underground to one another.
You have to be very careful with this as many of the tiles may turn into something other than what you expect and special land tiles may be need to be changed as well.
I put this in by request of users but personaly I don't think it will be of great use but here it is anyway.
Only version 1.0.1 or higher of Divine Right will be able to activate this code.