In fact you can "fix" the error message about the NNID being already on other console by doing the following instructions. After following them, your games tied to your NNID won't be visible anymore in the home menu, but you can simply use CIAngel for reinstalling the ticket (after accessing the eShop with the NNID removed), and they'll appear again in the home menu.
Situation Not Resolved:
- If the issue persists for more than 24 hours, go to the system's HOME menu. Select “System Settings,” then select “Nintendo Network ID Settings.”
- Select “Sign In.” Enter the password associated to the Nintendo Network ID, then “Confirm.”
- The error message (“You cannot use this Nintendo Network ID on this console”) will appear on the screen.
- While the error message is onscreen, hold down the X button AND Y button, and tap “OK.”
- Select “Yes” to unlink the Nintendo Network ID from the system.
- You will receive a message that the NNID link has been removed. Tap “OK” to return to the system settings.
- You can now re-link the Nintendo Network ID to the system, which should resolve the issue. How to
- Purchases associated to the system / NNID will still be available for re-download. More info
Extracted from:
http://en-americas-support.nintendo.com/app/answers/detail/a_id/13777/~/error-message:-you-cannot-use-this-nintendo-network-id-on-this-system
Still, I think it's a lot easier to backup your NAND, format without SD card inserted, buy LoE, do the transfer without NNID. After the transfer, relink NNID on source console, and restore NAND backup then. You're done, no need to wait a full week, nor to call Nintendo, and your NNID is intact and working in your source console.
