It's possible, I just doubt no one has the want or time to actually make it. It's just a matter of looking up ROM info and figure out where the maps are actually stored. If it wasn't possible at all, you wouldn't have tools that edit maps in Pokemon. And I know Dargor, the guy who's working on the FFVI SDK, made a map importer for the SNES ROM of the game. But it's a lot of work, time, and trial and error so best of luck. My honest suggestion is to go to
http://spriters-resource.com/ and see if you can't find tilesets there for your game.