When you sign up to be a voting delegate to the state convention you take a pledge not to vote for a different candidate than the one chosen.
Theses treasonous fake Rs aren’t delegates though. I think any candidate running for office for the Republican Party needs to sign a pledge supporting conservative principles - if they ever subsequently support any other party or non-Republican candidate without resigning from the party then they should be expelled publicly so they can’t claim to still be a Republican yet be a speaker at the Dem convention for example.