I think something along the model of the Conservative Party in NY could be effective if implemented nationwide.
That is, build a separate, parallel structure that puts up and supports a slate of MAGA/tea party/conservative GOP candidates in every district. For those few states that allow candidates to run on multiple party lines (like NY), establish immediate parties. For the rest of the states, wait a few election cycles until the new “party” apparatus is staffed, functional and effective. Then, file within the remaining states with the “new” party.
That’s an interesting idea. Basically you’re talking about a separate, independent party structure devoted to vetting Republican candidates. That has some potential.