On June 16, the Vermont legislature passed HB 474. It says someone who loses a major party primary may not then qualify as the nominee of a minor party, or as an independent. Also it says write-ins will no longer be counted unless the candidate has filed a declaration of write-in candidacy before the election. For general election write-in candidates, the deadline is the Thursday before the general election. Here is the text of the bill, which is an omnibus bill with many other provisions.
The “sore loser” part of the bill appears to apply to independent presidential candidates, but not minor party presidential candidates. It says, “A candidate who loses a major party primary for any office shall not appear on the general election ballot as an independent candidate for the same office for which the candidate lost in the primary election.”
UPDATE: Governor Phil Scott signed the bill on June 25.