Just to hammer the point even harder:
There is no such thing as a “registered residence”.
Each state or country will determine whether you are a resident, whether you must pay taxes, etc. based on the criteria in their laws. From earlier posts, it appears that criteria is “where you spend the majority of your time and live your life” not where you work. To get nitpicky, the example was 183 days ( >half a year) as a cut-off.
You don’t have to “register” this. You can tell the DMV and tax department whatever you want; if they decide to challenge it, you can pay a lawyer to argue whatever you want, and a judge will decide. However, in the event of a dispute, there may be legal and financial consequences.
You can have as many homes as you want, all over the country; own, rent, or a combination; (McCain got raked over the coals politically for having what, 11 houses?) occupy, rent out, or store a hoarder-load of junk. Whose name is on the title or leases is totally irrelevant. Only one can be your primary residence. See point #2 above. Normally, unless your time is fairly evenly split (or you have and use 11 homes), it will be obvious which is your “home”.
Some DMV and insurance companies will get upset over a vehicle that appears to spend the majority of its time in their state but is registered in another. This could result in insurance claims being denied, tickets or fines for failure to properly register or for evading taxes, etc. You could be charged with voter fraud if the DA and judge decide you are not eligible to have cast a vote and you did.
I’m reminded of the Mark Twain quote:
MT: “How many legs does a dog have if we call the tail a leg too?”
Set-up Guy: “Five?”
MT: “No, four. Just because you call a tail a leg doesn’t make it one.”
You can call your primary residence (not “registered”) whatever you want. However, if the MA Tax Department or DMV or whomever does not agree with your reasons why, their reasons will prevail.