If you wish to register as an “independent” make sure you register as “unenrolled”!
“Secretary of State William Galvin said he is concerned that as many as 20,000 people who meant to register as “unenrolled” instead mistakenly registered for the United Independent Party, a party established by Evan Falchuk, an attorney who ran for governor of Massachusetts in 2014.
“If you’re registered as an unenrolled voter, you can choose which party ballot to pull on primary day. But if you’re registered with a specific party, you can only vote in that party’s primary. There is no candidate running for president from the United Independent Party.”
—Thousands Of Mass. Voters May Have Accidentally Lost Their Ability To Vote In The Primary – WBUR
You will only be able to vote for the nominees in the party with which you registered.
Your choices are: Democrat, Republican, unenrolled, and United Independent Party.
Only as an “unenrolled” voter will you be allowed to choose which party’s candidates you will be voting for when you show up at the polls.
Please see the WBUR story, quoted above, for more detail.