I have to say that this is one are where I'm not sure I quite agree with Tesla's policies
as I currently understand them, which is admittedly based on limited information.
As was mentioned, the terms of liability release are important. If there really is a clause that states Tesla can confiscate the car with no compensation, then that's outright unacceptable.
However, as others have pointed out, repair and state-certified inspection is possible outside Tesla's purview, yet they disallow it. What's more they are reportedly refusing to even allow a person to even enable the hardware they own, or apparently sell them parts.
What authority should Tesla have to tell a person they can't this for the exercise... or to use it on private property (unlikely, but it illustrates the point).
Part of my opinion on this is based on
Otmar's Experience wherein he was undertaking a salvage repair of a Model S in an extremely responsible way, with the subsequent plans to use the drive-train parts for another project. Tesla Corporate ultimately directed local service centers to not sell him parts, and there's reason to believe he could face similar roadblocks in getting the car to supercharge. It could perhaps even be disabled over the air.
I think reasonable support of 3rd party repair is ultimately going to be necessary. Sell the parts at least.. but if ultimately they will not (or can not), then remotely disabling a vehicle that may have been repaired elsewhere seems onerous. There should be no liability to Tesla for a (salvaged) vehicle that was repaired elsewhere and passed certified inspection.