Tesla can see it being done, yes. They certainly can probably do and threaten to do a whole bunch of stuff, but legality of much they threaten is unknown.So Tesla can obviously easily see whether a vehicle is running software it isn't supposed to. Would people doing this risk being banned, lose supercharging access, warranty, etc? Are there any terms that state touching your own car is not allowed?
So far I have not seen supercharging access being threatened, at most firmware updates were on the table as being removed. Obviously don't get into any accidents too