Last year, we were in the same situation. We needed to assign a new MMSI number and change the boat
name for a Nuaticast that came with the the newly purchased boat
.. For the base formatting (MMSI and boat name) you will need the disk assigned to an ACR dealer. The new Austrian manufacturer has been calling them back and claiming these units are unalterable. We were in a hurry move the boat, we gave up and replaced it. The programming does not appear that sophisticated and probably is hackable with time. As long as you end up broadcasting info that is recorded on the vessel registry, you should be fine To be totally legit, you should probably do it offshore
which is why the new company wants you to send it to Austria!!
Good luck, John