Perhaps a better plan has since been drafted? One would certainly hope so.
By "previously" we could be talking 1953 here.
It could be worse than that. Our past two opponents were Hussein's Iraq and the Taliban.
Iraq is a desert country with a highly centralized population along the Tigris/Euphrates river valley. This combines to give a swift moving distance engaging force with air dominance a huge advantage. Of course that Hussein was the clown prince of misunderestimation helped.
The Taliban were in a mountainous country with little technology, no artillery, no infrastructure, and a population who supports whoever seems to be winning.
North Korea militarily has dated but servicable equipment, mountainous terrain, 10,000 pieces of artillery, a navy, a air force, a special operations component. NBC warfare capability (questionable on th "N" though). A population that may or may not support their opressors.
Further North Korea could wipe out Seoul, South Korea with the 3,000 to 4,000 artillery pieces in range.
Our side (counting South Korea, Japanese, and USA as our side) could lose the amount mentioned in the first few hours of the war.
The question is what would be the war aims of North Korea?
Completely taking over South Korea would be beyond the North's capability by itself. Destroyning Seoul and negotiating an end to hostilities is much more likely.