Are you intending to buy the car from the owner or the insurance company? If you buy it from the owner then it should not have a salvage title. Also, you should get the owner to insist that the body shop return it to him (you) as they found it.
The current owner has a contract with the body shop; Tesla is not part of that contract so it should not be able to tell the body shop to do anything and certainly not to “disable” anything. Current owner could ask the body shop, “who is paying you? Me or Tesla? Who is your contract with, me or Tesla? Who will have the right to sue you if you damage their property, me or Tesla?” That might help them understand their problem if they follow Tesla’s supposed instructions.
That said, I’ve never heard of anything like this so I wonder if this body shop is just trying to scare you off/drive down the sale price so they can buy it on the cheap.
Typically salvage cars are paid off by the insurance company and sold through a salvage auction like Copart or IAA. If the owner was at fault and didn’t have collision insurance then he can sell it however he likes, even as is, where is at a body shop.