If you want to edit model textures, then you can use JHLMV that I posted.
If you want to decompile the model and edit something in there, then you would need milkshape..
Milkshape is a trial though and you would have to buy it, but if you don't need it much, you can download the trial here:
Posted by V!nKu
Jed's Half-Life Model Viewer 1.35 .
You will find it here:
This is a VIEWER not editor.
Thanks for trying.
it can import and export textures.
So you can export the original, edit it with paint if you're a nubcake and import the edited. Then save as a diff model. (like T_guerilla_admin or something.)
Then you code the admin skins, but I dunno how to do that.