The North Korean Government is not exactly showing neighborly good manners right now, and it seems the various voices in the international media think these intentions are to do something to "get the attention" of the incoming American government.
Could also be that the North Korean regime is really, really, annoyingly, persistently, with-out-fail stupid.
Sure, they could cause a lot of damage to the Republic of Korea; Shortly thereafter the ROK Armed Forces would come north with an attitude not seen since the Soviets got into German territory at the end of WWII.
Bets are the North Koreans know that too. I say they are bluffing.