The problem in MS was that those specifically invited to participate had, in many cases, already voted in the Democrat primary. That was against the state's own rules.
Yes, I know. Mississippi had other issues.
The law can still be changed. A good argument for changing it might be that the way it is, it is an open invitation to this kind of fraud. Or else the Republican Party could decide to fund its own primaries, if that is the law in MS, and thereby keep them closed.
My mother taught me long ago not to leave your money or possessions anywhere where they might tempt thieves. Don’t lead a weak person into temptation, even unwittingly.