Agree that things may have moved on. My experience is that I bought my first Tesla (pre-owned) in September 2016. Tesla Birmingham made up suitable plates with my cherished number and fitted them FOC once I had made the necessary transfer. Inter3esting that the only 'fail' on my MOT in November 2018 was that two of the numbers on the plate they supplied were 8mm too close together. Not sure whether this was new regulation or what. When I changed in June 2019, Tesla transferred the cherished number from the old to the new MS and I collected the car fully registered and adorned.
As an aside, my own experience with Tesla Birmingham over the course of the last 5 years+ has been absolutely exemplary. Matters concerning them have been arranging repair for an accident (not my fault), replacement door handle, a new rear motor and car completely immobilised due to a software update glitch.