What part of the body.vtf file would I alter to make the fore-arms have skin and have rolled up sleeves?

You can't.

That would be a model alteration, not a skin.

Originally posted by Wile E Coyote
You can't.

That would be a model alteration, not a skin.

Wouldn't it be possible to use normal maps to make a kind of rolled sleeve thing?

Originally posted by Disciple
Wouldn't it be possible to use normal maps to make a kind of rolled sleeve thing?

In short No.

Normal maps don't alter the geometry of the underlying mesh, just create the illusion of it by altering the lighting on pixels in the texture. There comes a point where you reach a certain angle and the normal map illusion breaks down, usually when your looking at a face almost parallel rather than perpendicular.