A "behind-the-scenes 'regime change'" of the DPRK by the US seems ambitious and unlikely. It's not like previous communist governments. We can't construct a "Brigade 2506" style government-in-exile because there are no powerful exiles and the populace as a whole is extremely mistrusting of anything foreign, and even if we could, it would be bay of pigs x1000. We can't rig a Diem style referendum because there will never be any such referendum and even if there were, we can barely get intelligence on the inner workings of the Kim regime, let alone influence the "political process."

The best that we could ever hope for is some military coup by an existing general who already has inclination to do so, and that maybe such a guy is sympathetic to Chinese-style reforms and might enact some kind of Korean Perestroika. And if that ever happens, a lot of people are going to die, and it is going to be a transition that involves nuclear weapons changing hands from people who are being ousted from power. It's going to be scary.