Preparing Luigi's Mansion 3DS for resale

I'm considering selling my old blue 3DS to help fund a New 3DS. The 3DS I bought was the one that came bundled with Luigi's Mansion (an uninspired move on my part) and I want to remove my personal data from the console without deleting that game, to add to the value.
My question is: is this possible? Or when I registered my NNID with the console did I eliminate any chance of this working out?
Best Answer
Even if it's not possible through official means, there are other ways. There are ways to install custom firmware on every 3DS in existence, on any firmware version. This is very much unsupported by Nintendo (they condemn the practice) but it will enable you to unlink your NNID while keeping the game on the system.
I'm not a lawyer, but despite what Nintendo's EULA says, I'm pretty sure selling the console like this, at least in the United States, is legal due to first-sale doctrine. Just don't retain a copy of the game or redownload it from the eShop, unless you're okay with piracy and are willing to take the (probably extremely small) risk of being sued. Also, if you decide to go this route, you should explain in the product description what you did, just so the buyer is aware they won't be able to link the game to their own NNID.
See https://3ds.hacks.guide for instructions on installing custom firmware.
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How do you clear a 3DS to sell?
Tap Format again to erase the data.Luigi Fails At Cooking
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