It was apparently posted back in April on GBATemp, but being that I just learned of it today, I wonder who else hasn't seen this. It works on both the old and New 3DS, though I have only personally tested this on an old 3DSXL running 9.2 FW and it does work, great I might add.
OLD 3DS METHOD
Download the code.bin
Copy it to the root of your SD card
Launch the web browser
Clear cookies and history
Go to loadcode.projectpokemon.org
Wait for the load bar and the message "failed to load" to disappear
Press Home
Done !
Do you want emuNAND support?
Of course... never.
We have two possibilities for emuNAND support :
-Gateway add support for patching NIM directly in their firmware
-You swap tickets, and install with a CIA.
Credits to yifanlu for the offset and the nop slide.
LIMITATIONS :
It's now stable.
Set your internet connection BEFORE and make sure it's valid.
Access the service you want after you see "finish" in the debugger.
Tested with :
-eShop
-eShop in games (update of Mii Plaza, DLCs, etc.)
-System Transfer (but the source and the target need to have a firmware in the compatiblity list) ---> a whole system transfer has been tested and it work!
-Theme Shop
Original GBATemp Post
Also, I cannot be held responsible for any damage this may or may not cause, and any and all issues should be posted on the GBATemp link, as I did not code this and cannot provide support.