If they really wanted to do that, it wouldn't be very hard; they'd just do something like what the UK did: set themselves up as permanent monarchs (of a sort) a

If they really wanted to do that, it wouldn't be very hard; they'd just do something like what the UK did: set themselves up as permanent monarchs (of a sort) and then set up a parliament and gradually shift power to it while keeping the Kim dynasty as head-of-state. Make sure to write the laws so they can't be applied retroactively, eventually make the Kims figureheads who just sign the laws and act as a possible last-resort in case the parliament goes out of control or does something they really don't like, but otherwise stay out of governing. No, I think the dynasty stays in power because they actually want to be in power.