You can.
If you don't want the ashenvale cliffs, use the dungeon tileset as basic, and modifiy it to have all the ashenvale tiles in there too.
But i guess you want to be able to use both cliffs.
Therefore you might try the WE-Unlimited. I think i may remeber that this was possible in there - no shure about that.
The last way is, that you could 'simply' export the dungeon cliff texture and reimport it to replace on of the ahsenvales.
I guess that's all possibilities. (maybe you can do it with some triggers too - no shure about that either)
i hope this helps you a little ^^
- Raszul
