i have a huge building with a lightmapped/bumped-specular material. I got 2 UV. UV1 (tilling) is for the diffuse. UV2 (unwrap) is for the lightmap. Unity automatically affect bumpmap to UV1, but i want to use it on the UV2 to draw scars on the building, how can i do this ? Does it possible to choose the uv channel for each texture of a material ?
Sure, just duplicate/edit the shader to fit your needs. Download the source of the shaders (it's on unitywiki, probably on unity's site as well) and copy/paste the content of the lightmapped/bumped-specular shader into a new shader, edit away.
In time, don't be afraid of editing shaders. They're quite simple to understand and tweak - not to mention extremely powerful.