Boat registration reciprocity is not unrestricted. I believe NH allows you to operate an out of state boat for up to 30 days without registering it in NH. This period is not an interstate standard. For instance, Florida allows 90 days.
If you behave yourself you could probably get away with a full season on NH waters without having to get a 2nd registration. I know that I have observed a few Mass boats tied up to docks all season. Of course, it's possible they have the paper work on board and just don't bother to install another set of numbers.
And that's all I think I know about that...
Good luck and enjoy your visit!
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