Make sure you modified the secureinfo_a in the EmuNAND appropriately prior to doing this.
You can try the 3 sd card trick as detailed in this post under how to get on eshop:
https://gbatemp.net/threads/3ds-region-change-tutorial-easy-way.386207/
Basically you need 3 emunands on 3 sd cards as follows:
1) EUR EmuNAND with NNID signed in
2) EUR EmuNAND with no NNID signed in
3) JAP EmuNAND with no NNID signed in
You already have #3, so I would create #2 first then #1.
Once you have this follow these steps:
Step 8: With the 1st SD Card, set up an NNID. BUT DON'T SET IT UP ON THE 2ND SD CARD.
Step 9: After setting it up, launch the eShop. Set it up as usual. While on the main page, press HOME and close it off. Turn off the 3DS.
Step 10: Use the 2nd SD Card you didn't set up an Nintendo Network ID with, and launch eShop. It'll say an error message. When you see the error message, TURN OFF the 3DS. This is very important.
Step 11: Now use the 3rd SD Card with another region. Launch the eShop. Aw, it worked! Great job!