The MMSI number stays with the radio and can’t be changed. Go to the BoatUS MMSI site and fill out the transfer paperwork. If the previous owner has not reported the boat sold to release the number, you can claim it by providing proof of purchase. Easy process, quick turnaround.
We have found out that if the MMSI number is Registered in USA and you import the boat to another Country, you must change the MMSI number. The Government requires this. People will do it and it costs about $150 CDN 🙈
I sent me RayMarine VHF back to RayMarine, they wiped and put in my MMSI, updated a few components all for free, including shipping. They are located in NH.