Actually, it is a bad idea. It’s a terrible idea. If one were to redraw the maps based on party registrations of people not unusually likely to vote for one’s party in the general election, one would find oneself, uh, surprised (and unemployed) come election day. If one signed up a ton of people for primaries who didn’t share at least some of one’s party’s platform, one might find onesself with unorthodox primary winners and reduced control over the party (not necessarily a bad thing, mind you, but a dumb one if one is a party boss).
I have no reason to doubt the story’s veracity, but this sounds like a few boneheads doing something wrong that is also not in their party’s best interest. It seems to me that a person who believes that something like this is sanctioned by the party’s leaders would have to abandon any conspiracy theories they might have had, as the leaders would be too dumb to put such a conspiracy together.