First you have to take over the GOP state committee, and then change the primary method. If you go to caucuses, at least everyone participating would be Republicans.
If Ruth Buzzy Geezer would hurry up and croak then Trump could replace her now. Then in ‘18 we could kick out the RINOS even if it would mean 2 years without control. As soon as(if) Dems take over old Ruthy girl will take a powder, bet on it.