He keeps his hair the same way his grandfather did. With all the portraits everywhere it gives him more legitimacy as heir. (It might be some theory from something I watched or read, but it seems plausible; Why else would he have his hair like that).
One assassination here, a demotion there. He is fixing his power. There is a rule in NK set by his grandfather that only his heirs are allowed power; and Un is weeding out contenders. That's also why he has silly hair BTW.
He seems to be planning to rule for longer than the other rocket man with many more rockets.