Imma playa ;P
I doubt i weill ever use RPG XP, i think after my hack/if its going to be completed sometimes, Im out probably than.
For that just take both mountains, add em to 1 image, index or try to make the pallete lower on your own(Example: remove some brown pallettes that arent that necessary anyways to make it use less brown palletes, or grass etc). and get Charakter maker 1999 if you don't have it.
Than take the png to charakter maker after opening and you see a tab how much palettes it has[the first colour should always be bright one thats going to eb the first on that tab for the transparency].
Adn if it only onw row than save the pallete as an act file and load it in a-map on the pallete you want to edit, and export the tileset, insert the tiles and import again, and vuola there in ;P