Full terrain editing : Sunken Ruins

[Razengami]

Hello, i'm making a map in which you are in a big naga temple, but since i use many custom naga models, i'd like to change the color of the sunken ruins ... changing the yellow to grey.. if possible i'd like to change the terrain tiles, the terrain mountains for ruins, the stair-like doodads and some other models...
Here's a list of the models/things i'd like to change:

- Sunken Ruins terrain textures "Large Bricks"
- Sunken Ruins cliff type "Ruined Walls"
- all Ramps for Sunken Ruins that look like the terrain
- all Stairs in Sunken Ruins
- all doors in Sunken Ruins
- naga ruins circle

i know it's a big request, and i'd love to do it by myself not to bother people with something big like this, but ive been looking everywhere and i couldnt find how to modify terrain tiles skin ...