changing secondary texture dynamically?

I want to change the texture of a secondary material on my 3d model ( a smiley face, in this case). When I use renderer.material.mainTexture, it changes the base texture of my model, and not the face texture Here is a screenshot of what my current texture/material set up is. ![alt text][1] So, when I apply mainTexture = xyzTexture (example), the Texture of "body" gets changed whereas I want to change the texture of "happy" Anyone know any way to do this? [1]: /storage/temp/15808-untitled.png