head modding query?

I am going to mod a chavo head (I think) to make an estrada figure. Id like to know how to do this...

I want to change his forhead shape to make it slighly rounder...can this be done with sanding?

Also how do I add things to the head...can I use "green-stuff"? Or is there something else I could use.

Any other tips would be appreciated

Thanks