why cant he just take his name off and then come back later?
I believe it would invalidate his vote for 2018 if he changed his registration this late.
Here's an article on this citing NY's arcane election laws.
Opinion | Ocasio-Cortez Isn’t Spelled C-r-o-w-l-e-y
That said, the arcane election laws that could keep Mr. Crowley on the Working Families line do need to be changed. Legally, candidates’ names can be removed from a party line only if they move out of New York State, die or accept that party’s nomination for a different office. Mr. Crowley has said, understandably, that the first two options hold no appeal.
Bill Lipton, state director of the Working Families Party, said he asked Mr. Crowley to consider the third option. Mr. Crowley declined, saying on Thursday that he felt accepting the nomination of the Working Families Party for another office elsewhere in the state was akin to election fraud, since it suggests to voters he is running for an office he has no intention to occupy.
If Mr. Crowley means what he says, his presence on the November ballot is unlikely to have much of an impact since New York’s 14th Congressional District, which covers parts of Queens and the Bronx, is overwhelmingly Democratic. Ms. Ocasio-Cortez has also become extremely well known and popular. But the episode is a grating reminder of the brokenness of the state’s election laws.
New York makes it difficult to vote at nearly every turn. It is one of a minority of states in which there is
no early voting, despite a broad push by good government groups and others. Residents must register to vote 25 days before every Election Day — that’s compared with seven days ahead in states like Connecticut and same-day voter registration in states like Colorado.
New York also requires voters who want to change parties to do so
more than a year before an election. And it maintains a stockpile of outdated voting machines that have been known to break down, gumming up elections. In 2016, New York City’s Board of Elections wrongfully purged at least 117,000 Democratic voters from the rolls. Reforming the City Board of Elections requires changes to state law.
Jerry H. Goldfeder, a well-known election lawyer, said New York’s election laws are “extremely, uniquely peculiar.”
“They need a total revamping to make it easier for voters to understand, for candidates to run and to make sure the winners reflect the preferences of the voters,” Mr. Goldfeder said.
Fixing this will require action from the State Legislature and the governor. If Democrats
win control of the State Senate this November, a unified state government should get it done.