Unity Assign Texture to Material in All Scenes (JS)

So I have a material applied to a wall in all scenes which has no texture but is transparent.

How do I code a Javascript script which will enable me to change the texture of not the wall object (with that material) e.g.

 var Mat : Material;
 var texture : Texture;
 function OnMouseDown () {
 Mat.renderer.material.mainTexture = texture;
 }

but also to the actual material in the Project View so that all of the walls in all the scenes will have a different texture, not just one scene?