Elon's email:
"Yeah, I have now insisted that even the tiniest (this was obviously not tiny) change to the car requires a physical inspection and buy off from me. The headliner change shouldn’t have happened.
The exact price of the P+ retrofit is still tbd. It would be $6500 plus whatever the labor cost is. Unfortunately, this is a major operation, so labor cost is high -- $8500 to $9500 is about right.
Tesla cannot do partial upgrades, as we have to test the heck out of anything that we provide as a manufacturer for regulatory compliance and liability. However, as an end customer, you are allowed to do whatever you want to your car, even if not FMVSS compliant."
I think we can order the suspension bits and the rear rims separately...as far as I can tell. It should be possible. I will try to just do the suspension first.