"Non programmability of the MMSI is a US specific legal
Yes and no. Apparently the folks at Nautilus (Lifeline VHS) have dealt with this. If your Nautilus unit has an MMSI number programmed into it, and you need to change that? You contact Nautilus, they send you a software
upload, and that wipes out the old number and allows you to start from scratch. Proving, it most certainly IS possible.
And they even have specific instructions for how to obtain an MMSI for a unit that is NOT attached to a specific vessel, since their units are designed for "portable" personal use.
Legalities? Damfino, but they're making it work.