I do not know official rules. I have climbed with many, many USAF men and women in Korea over the years (Army people, too). None has worn a helmet consistently, however, if you have it, bring it.
I (most of us) go by the rule of wearing them at crags where there is loose rock (a good rule to follow: if everyone else is wearing one. . . ) and on multi-pitch climbs. Also, as you are coming in Feb, there is ice to consider.
No one will be at the crags to check on you. Apparently it is illegal for under 21 USA military to drink (despite being legal in Korea) or go to Jjimjilbangs. No one in the climbing community is here to police you. We may even lead you astray.
"If you can't do something well, you might as well learn to enjoy doing it poorly."
-- from a de-motivational poster, but I find it oddly liberating