Here are Miis that I decided to switch their badges and the reason.
Joseph (from Wii Sports Club Track Edit) <=> Marit (from American Miis Track Edit)
Why ? : We now know Joseph's nationality because of the Mario Kart 8 Deluxe Overview Trailer, I switched him with a Mii (Marit) that nobody knows her real nationality. (Joseph and Marit will still match with one of them category)
Naomi (from American Miis Track Edit) <=> Ian (from Splatoon 2 CPUs Track Edit)
Why ? : Ian's name sounds more American that Naomi's (Naomi's name sounds Japanese) + Naomi is a Splatoon 2 CPU and Ian isn't. (I switch Naomi and Ian to make sure Naomi match with one of her category.)
Ian (elderly Naomi) <=> Skip (from Guest Mii Track Edit)
Why ? : We have the proof that Skip is American so I switch his badge to make sure Skip match with one of his category