How do I change the 3DS eShop region?
Solution 1:
You don't have to delete your current one, but you do have to create a new one. According to nintendo support, "Nintendo 3DS family systems can only support one Nintendo Network ID at a time. However, you can format the system to deactivate the current NNID and create a new one. (The existing account and purchases will not be deleted, and can still be re-linked to the same system in the future.)"
Also, it is necessary for the system and NNID country to be the same. Other useful information can be found here.