He's correct, referral is only for new customers, existing customers can't use referral. Just try using it and see what happens. This isn't that hard folks.
Max PSI. The reason is the Pirellis are Passenger tires and the Goodyears are Light Truck. Light Truck tires have a higher ply rating and are usually 80 PSI Max. Passenger tires have a lower ply rating and are usually 44-51 PSI Max.
This is why Tesla doesn't put it in the owners manual. People like the hoi polloi are too dumb to understand the difference between soc for battery health and maximum soc for road trips.