Requirements
1 Both system MUST be at LATEST firmware transfer requires online update of both console via Nintendo server, no way around this.
2 Both systems must be on same region no cross region transfers, it won't even detect the other console if regions don't match.
3 After transfer your source nand is wiped, nand backup will work but all your games will be offline only since NNID will be migrated to a new console in other words you can't have two identical systems NNID can only be linked to one.
4 To keep your GW functions update only from Emunand.
5 You do not need 2 GW cards for emunand to Emunand you can enter emunand via MT launcher with no card in classic mode.
Here are all possible transfer scenarios all have been confirmed to work.
Sysnand to Sysnand
Sysnand to Emunand
Emunand to Sysnand
Emunand to Emunand
Emunand to Emunand
With the release of the 9.2 exploit, I wanted to move my "official" 3DS profile from my 4.5 launch 3DS to my Zelda 3DS XL. So I did. It wasn't super simple and there was at least two panic moments; but here's what I had to do to make it work...
1 - As with any system transfer, both systems must be of the same region and on the highest firmware. In this case both EmuNANDs were on 9.4 US.
2 - Initiate the system transfer from within the EmuNAND (GW) system settings on both devices. Operation proceeds as normal for a system transfer.
3 - When the initial phase of the transfer is complete, things get dicey. Both systems need to reboot. But doing that dumps you to SysNAND on them both. And the TARGET system reboots into the system transfer section of the system settings, and fails out. Well, don't panic yet. Just shut down both systems.
4 - At this point you are also supposed to move the SD card from the source system to the target system. The problem is that this SD card has the wrong EmuNAND on it now. Remove both SD cards. Don't get them mixed up. You have two options:
a - If you wish to use the SD card that was in the TARGET system, copy the files from the SOURCE SD to the TARGET SD using your computer. Simple as that.
b - If you wish to use the SD card that was in the SOURCE system, you must extract the EmuNAND partition from the TARGET SD card, inject it into the SOURCE SD card and then put the SOURCE SD card into the TARGET system.
(If you wish to continue to use EmuNAND on the SOURCE system, just do a format EmuNAND from the GW menu on it, or restore an old backup. No need to complete that process normally).
5 - Now, on the TARGET system with the correct EmuNAND installed in the SD, launch the GW exploit. The system will boot to the EmuNAND system settings and try to complete the transfer. For me, this always failed and dumped me back to SysNAND. To get past that, I had to disable Wifi as it booted into GW mode and then tell it to NOT continue the transfer and abort.
EDIT: I did this again between another set of 3DS's. This time I didn't get any errors on step 5 and it just completed normally. That may happen too, which I guess is better and easier? But either way you should be able to finish it. If this proceeds normally, you shouldn't have to mess with step 6.
6 - Dumped back to SysNAND again, and again launched the GW exploit, this time I was taken to my EmuNAND home screen. However, none of my installed software showed. I launched the eShop and after about 5 minutes of waiting I was able to finally log back in as my NNID HAD transferred. After logging into the eShop and returning to the Home menu, all my installed software showed up again in wrapped presents (and was also available on the eshop as redownloadable if needed).
So in short, it worked, but I had to interrupt the process, transfer my EmuNAND partition and log into the eShop to validate/finish the transfer.
This was from 3DSs that had a physical wifi switch to interrupt the process. Since wifi is necessary to launch the exploit on 2DS and I'm assuming N3DS, and neither of those systems have a point where you can disable the wifi in software during the process, I assume the same could be accomplished by disabling your home wifi at the appropriate time. But don't quote me on that.
All your account info and legit purchases are now stored on a fickle SD card. MAKE AN EMUNAND BACKUP. THEN MAKE 3 MORE AND STORE THEM IN DIFFERENT PLACES.