Indeed the fighting ended in an armistice so the war was never legally declared to be over. Visiting the DMZ between the countries is a surreal experience - part tense stand-off, part theme park.
Whenever North Korea threatens them, simply reply with how sorry you are their brother nation feels this way, and you wish them a peaceful and successful future.
Leave the DMZ intact of course, but just unilaterally declare you are not actually at war and have nothing but brotherly love for them.