I doubt they can force you to register a USCG documented boat that is from another state just because you've brought it into the state's waters, unless you've been there over 90 days... My boat is USCG documented, but not state registered, since Massachusetts doesn't require you to state register a documented boat.....
But Mass does have use taxes, which may be why they don't bother with the nickle and dime registration fees. Let's face it, registration is simply about collecting a fee for the state. I was told that Mass marinas are required to report all vessel on their moorings or slips for two or more weeks. Is that true?
I did not have to pay sales tax in RI, since they have none on boats. I do pay $300 per year in registration fees instead. Of course, it will be roughly 100 years before that breaks even.