Change texture (cycles) of a linked character.

I have a character that I will use on a number of scenes for a 4min short. So, I make a base one and linked it on the scenes, works like a charm, I could make a proxy of the armature and animate it, the problem is the texture of the material, the mouth of my character are .png sequences, one for each scene.

How can I use this linked character and change this mounth texture? :confused:

Materials can be linked either to object data (default) or object. When the association is set to object the material slot order counts.

Source file:

Target file:

Could make the material local and change the texture. Object data (mesh) still comes from linked library, as does the other material, but the material association is on object so it can be changed.

How can I make only material that I want local?

One more thing, my character is inside of a group, as its made from a bunch of separate objects.