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While I don't know for sure of course, I can't see why they wouldn't? Automakers make good change on selling accessories, and Tesla has made options available to Roadster owners.
While there's been some speculation regarding whether or not Tesla will offer upgrades as new versions of the S get introduced, wheels and rear cover are simple accessories and there's no visible reason why they wouldn't be available.
Now, how SOON after deliveries begin will they start selling accessories is a better question IMO.
Also -- if your state waives sales tax on EV purchases, then any accessories you buy at the same time as the EV will also be tax-exempt. Later accessory purchases, however, would not. (That's my understanding, anyway.)
But to answer the OP's question, yes you can buy stuff later w/ the Roadster. Things like wheels, CF accents, suspension upgrades, etc. Basically if you're willing to pay for it Tesla will install it.
I wouldn't count on post-delivery suspension upgrades -- that's a lot more than just swapping out wheels or even interior accents. I wouldn't take experience from the Roadster as precedent for the level of customization Tesla is going to be willing to do on a Model S after it's been built. The only things that I'm confident will be available after delivery are wheels, the parcel shelf, rear-facing seats, and the HPC. Tesla has hinted that the second 10kW charger can also be retrofitted, but advise that you purchase what you're likely to need with the car.
Also -- if your state waives sales tax on EV purchases, then any accessories you buy at the same time as the EV will also be tax-exempt. Later accessory purchases, however, would not. (That's my understanding, anyway.)
This would be correct for WA. While the HPC is tax-free in WA regardless, time of purchase is definitely the time to throw in the winter tire package if planning on buying it anyway.