Renderer has a property called materials, which is an array containing all of the materials on one object. So since the eye material is the second one in your case, you may want to try
go2.renderer.materials[1] = myEyeMaterial;
If this is not the correct material try looping through the materials array and check the name or a reference to find the correct one.
Thanks guys. I had actually already tried it Pia’s way, but with no results at all. It wasn’t changing anything about the materials. But doing it with Eric’s syntax, where I temporarily store the materials in a var variable, it will actually work. Can someone please explain to me why this is?