The shady behaviour here is that they are framing this as 'updated terms' that people have to accept. Indeed this is quite aggressive and should cause whatever regulator/authorities to look into their practices.

Of course what they are actually doing is they are proposing new terms, which customers are free to refuse. The existing contracts stand and Tesla would need to follow whatever is permitted in the contract or contract law to cancel it or be liable for compensation.

I would also think that there ought to be an expectation of a reasonable deadline to execute the contract or customers can ask for a refund (at a minimum) and walk away, but IANA.