No, the best thing the rest of the country can do is demand military intervention.
When foreign nationals stage a hostile invasion of a state, that’s supposed to be the response of the United States.
It’s in the Constitution.
Talking about getting real creative I have been thinking that retired California Republicans can invite out of state retired relatives to share their homes several months per year during the election season that way the out of staters can share their relatives home and register to vote in California. The out of staters can help out with their families’ expenses and they can add to the Republican voter base.
Many retired northerners live part of the year in Florida so I don’t se why out of staters cannot move to California part of the year and register to vote in California?