To answer your last question, yes. And this new material that you've created will still be using the original uvs of that area on the bot.

For example, I use the group editor to create a new material in the shape of a headband on V4's forehead, an area that was originally defined by the SkinFace material zone. After having added the new material I notice that this area is no longer covered by the texture map that was applied before but is now colored an arbitrary color. OK. I go into the material room, scroll down to V4's SkinFace material, copy all, scroll to my new material, paste. The texture is applied to my new material. If I change the color to black in the diffuse chip, it will appear as though V4 is wearing a black headband (or more like a black headband shaped tattoo). Adding a new material is best for masking type techniques such as adding a patch for different specular, diffuse color, procedural makeup effects, etc. If you want to change the "painted" image map based texture of the area you will need to paint some new image maps using a UV template in an image editor or modify the original image with some procedural method.

Hope all of this makes sense, it's late and I'm a wee bit spaced out. :)

Edit: adding new material regions is a good way to make parts invisible via transparency, though. Perhaps what you're aiming to do.