Right now, FPSC has an 'alternate texture' feature. That is, when called on by a script, a texture will change into its alternate texture. However, there can only be one alternate texture.
I believe that your solution may not be in the texture. You might have to either do one of the following options due to the limitations of FPS Creator:
1) Increase the eye area's polygons so that you can attempt to animate it through the use of bones and skeletal animation.
Or-
2) Use a complex script to change between models with the different textures you want (i.e., you stated looking around, and facial expressions). This would have to be written so that it loads and hides models constantly.
Hope that helps, feel free to ask any questions.
-PwP-