Add just new media when you change your region priorities?

[FlightRisk]

I did not have "Japan" selected in my "options -> region priorities". So I added it and made my priorities, "North America, United States, World, Europe, Japan", in that order. I wanted to make sure that on games that had a Japanese version that I had, whether Arcade or something like Famicom, that I had that art. Maybe I don't understand how this works, but will it get both and display one? Or will it only get the top one it finds and only get Japan art if it can't find anything else? And since I did not do this in the beginning, do I need to delete all the media and scrape again, or "download metadata and media" and select "yes, but do not replace any existing fields or media"?