When I couldn't get a tire/wheel set from Tire Rack, I decided to go to plan B. I called the service center and explained that I was taking delivery of a CPO P85+, and couldn't/wouldn't consider driving home to middle NH on summer performance tires (this was before I realized it would be delivered). I explained that I understood they offered a winter wheel and tire package, but, given the roads conditions we deal with up here, I much preferred a Nordic winter tire (ie, Hakka R2's) than the performance winter tire they offer. I asked if I could bring a set of Hakka R2's in, buy wheels and sensors, and have them mounted and installed, and bring the 21's home in the trunk. The rep hesitated, I pointed out that these tires were the approved standard tire sold by Tesla in Norway. He then put me on hold to ask the service manager, who OK'ed it.
I sort of consider this a one-shot deal, because I'm getting a car in winter that normally comes with summer tires. I would not expect to bring my own tires on a regular basis and have them installed. I would buy tires from Tire Rack and have them shipped to a recommended installer, and bring in the car to them.
You could go to the SC, buy a set of wheels and TPMS and take them somewhere to have the tires mounted and installed, I suppose.
I think the SCs are much more sticklers on Tesla spec/sold wheels than tires, though it still depends a little on which SC, when you did the transaction, and how well you know them. I had a March 2013 S85 and didn't like how the Michelin all-seasons handled in the first snowfall Thanksgiving 2013. I decided on the Nokian R2s, bought them at a local chain (Direct Tire also in Watertown MA), and had Direct Tire install them on the original 19" rims with the existing TPMS sensors. The following spring I bought a set of unused 19" original rims on eBay and took them to the SC with my original tires, buying TPMS sensors and caps and paying for mounting and balancing. From that point on they just swapped them out for me every fall and spring.
I just had Direct Tire put Nokian WRG3 SUVs on my X 20" rims and am tempted to keep them on year round as they're an all-season tire with snow rating. But I may swap back to the Michelin Summer Sport next spring just to get some more miles out of them, they only have 8500 or so now (X was delivered March 30). I expect the SC would mount and balance them for me, but if not I'll go back to Direct Tire.