Thats exactly what i wanted to do with mine. i wanted to have the damaged arm removed and replaced by the full arm like yours, but that would entail me finding another clean version leather jacket as i already have my clean T-800 posed and displayed. The jackets on eBay go for crazy money!!!
I got my clean jacket here on the boards from Teddy Daniels for around $60, I really lucked out with that. I had to pay another $47 for the handgun on ebay though. I was really questioning my sanity when paying that price for such a small piece.