Help with retrieving/inputting a portrait.

One of the units I am working on now doesn't have a direct portrait. That is to say it is a different one from the skin, meaning that any changes I make to the .blp affects the in-game unit but not the portrait itself.

Using War3 Viewer, I've found that the texture for this particular unit is modeled off of the Priest. However, I am unclear on where to go from here. I extracted the portrait model but I don't have any programs that will allow me to "unwrap" it. Also, I would like to leave the actual Priest unit unchanged.

What can I do that will allow me to do this? Is there an unwrapping program that will change an .mdx into an editable .blp? For some reason no 3D modeling programs seem to work on my computer, so any model work beyond editing the .mdl with Notepad is out of the question. Is there a way I can import the .mdx portrait into my map in a way that will let my custom unit, and only that unit, use it?

Thanks for listening.