I bought a motorcycle years ago with a KIA (Northern Ireland) number on it. As I drove a Kia, it made sense to pop it on the car. What a pain it was.
Buy new plates, rearrange insurance for both vehicles, rearrange tax for both vehicles, waiting for documents etc. Then I bought another Kia and had to repeat the process every time I changed. Never again!
............ and at £80 to DVLA, £40 for plates, £25 admin fee for insurance???