This probably varies a lot by state. As you're in Rhode Island, I can comment, but my comment is: Be glad you're buying now that the Warwick store is open, rather than before. When I bought my Model 3, I had a choice of accepting home delivery with
no plates (so my car was taunting me in my driveway, legally undrivable until I could go to the DMV to get plates) or go to New York state to pick up a car with temporary NY plates and then deal with the RI DMV myself. I chose the former. Oh, and I had to walk uphill in snow both ways.
I've purchased (or leased) two cars in RI from RI dealers, prior to buying my Tesla. The first time, I transferred plates from my previous car. The dealer did that work. The second time was a lease, and as I kept my old car for a short period after starting my lease, I needed new plates. The dealer put temporary tags on the car, but also arranged to get the permanent plates. I had to take the car to the dealer once they'd gotten the permanent plates. Of course, that was a lease, so the procedure may have been a bit different from a purchase.
You'll probably just have to do whatever Tesla says, I'm afraid. Whether they
won't put permanent plates on the car or they
can't do so for some legal reason, you won't be able to force their hand. The Warwick store has been open for long enough that I doubt if you're running into something as simple as an uninformed salesperson.