OH, yes… there is a thread some where here about someone who did this exact same thing… but I dont know what to look for to find it.
If I remember correctly they did it with materials only… I havent studied that very much though.
You can use alpha in your uv images for the face. You could use the real properties in the uv/image editor and then make an image with certain movements, like an animated gif.
But you would have to swap out the image to the one needed for the situation. I think that would require python.
or, you could just have different meshes, and end/add the one needed for the moment.
Never tried it, just brain storming.
Since you can use multiple uv maps per mesh, even for the same planes, then perhaps this could be done just by adding a new image per each new map.
This creates layering of the images. Then perhaps somehow use these to tick through, instead of realtime properties as above.
But again it would require python. I think. And you probably dont mean to use this in the GE, but for rendering an animation? Sorry, Im always in the GE in my head.