I had obtained an Amateur Radio tag for my truck about a decade ago. It was quite an ordeal due to a lack of documentation at DMV, and their inability to be able to enter the request in their computer system. In fact, shortly after speaking with the director of the DMV at the time, a new form appeared that spelled out the process.
After 20 faithful years of service, I retired my truck this year and replaced it with a plug-hybrid. I was a tad concerned about getting the Amateur Radio tag converted over, but it was an easy process, all done at the dealer. The new plates showed up about 5 weeks later. All I had to do was pay the regular fee for obtaining a replacement tag (the old tags were beat up and did not identify it as a EV/HEV, which is important for fire services to know).