As a youth, I would visit several dozen homes, walking several kilometers, in the process. In Korea, you could visit a hundred homes or apartments without leaving a single building. That would bankrupt the families offering treats and overload the kids with sugar even from a Hallowe'en perspective. So it would be strange to knock on doors in Korea and expect people to know why you were there.
So one my fellow ex-pats in Korea created an event, Trunk or Treat, for the local foreigners. There were problems with ESL schools visiting and cleaning us out or expecting ESL assistance so we had to make the event on Facebook private.
But when it worked, it worked very well! Images from 2014's Busan Trunk or Treat event.
We all met early enough to park the cars in good light and not threaten the children we had brought with us. Then we decorated the cars. I always arrived too late for the games but before dark the kids had a few games and then when it was dark enough, the kids went car to car, having their costumes admired and asking for and receiving candy.
Here is a how-to, if you want to organize your own. Or ask me in the comments for details.