As the parent of a family account, can I region switch so my son can buy a game?
Eshop code from Amazon Japan is quite cheap compared to buying locally.
I think the process for this would be moving my account over to Japan, which would also move his, redeeming the eshop code on his account , then switching region back to our local one.
In order to prevent fraudulent use, the Nintendo eShop and My Nintendo Store for Japan will stop accepting credit cards issued overseas and PayPal accounts opened overseas from Tuesday, March 25, 2025.
For customers who have previously used overseas-issued credit cards or PayPal accounts opened overseas, we ask that you please use other payment methods, such as credit cards issued in Japan, from now on.
If you are getting game code, instead of gift cards, then this should be fine. It would still be better to have a separate JP account for logistics though, or in case Nintendo changes something in the future.
For gift cards, oji has explained the issue below. You get card for $10 and the game is of $9.99 so you are left with $0.01 and then can't change your region.
Then I have another warning for you. As long as an account has a positive balance, you cannot change its region. This is especially difficult with gift cards. So, as advised in another comment, it is better to have a separate account for this purpose.