For John, BLUF: Yes, taxpayers paying for Party Elections. Nothing to see here; just move along.
From the Commonwealth Secretary of State, Mr William Galvin, we have a page devoted to Registering and changing one's Registration.
As most of us know, in the election coming up, 1 March, when you walk in you get a ballot based upon your party affiliation, upon how you are registered (Republican, Democrat, etc). That said, if you are Unenrolled you have no ballot, but you can draw a ballot for one of the organized parties.
In the 1 March election there will be ballots for Republicans, Democrats, The Green Rainbow, and The United Independent Party. Rumor Control says the United Independent Party ballot is blank, so you can write in who you wish.♠
If, for some reason, you wish to go from your current party affiliation to another, so you can vote in the Primary for or against Donald Trump or Bernie Sanders, you can do it on line. One option is to go from being registered as a Democrat to being registered Unenrolled. Then you can pull a Republican Ballot on election day.
Here is the gouge from the Commonwealth Secretary of State:
In order to register to vote online, you must have a signature on file with the Registry of Motor Vehicles. If you currently have a Massachusetts driver's license or state ID card, you may use the online voter registration application to register, update your address, or change your party affiliation. Voter registration forms submitted online must be submitted by midnight on the date of the voter registration deadline.Here is the "official" notice from our Secretary of State:
NOTICE: The last day to register to vote in the March 1, 2016 Presidential Primaries, or to make changes to your registration, is Wednesday, February 10, 2016.Don't delay. Register now. Or change your registration to the Party that will give you a shot at influencing that delegate count for the Presidential Nominating Convention this Summer.
UPDATE: Added footnote. Regards — Cliff
♠ FYI as of 12/21/2015 348 individuals are registered as United Independent Party.