Rules? no. Gravity? Yes.
Which is more serious, posting a fake status on your friend's facebook site pretending to be him as a joke?
Or filing his tax return on TurboTax with your own bank account as the recipient?
However, in doing some more research, SCOTUS has found that state party-legislatures act as state officials when conducting primary elections, so there may well be something to this.
I'm just saying that, personally, I'd be more offended were it to occur in an actual election at the state or national level that had binding results. After all the discussion of a bartered convention and whatnot, it should be clear that primaries don't have nearly the gravity of binding elections.