It's not just serial, it also relies on the internal console ID and client certificates. All three are checked when authenticating with Nintendo's servers, and the client certificates are signed. There's no way to retrieve all three except without hacking another console, and you cannot replace them without IOSU access. It's the same situation on 3DS, which is how I know they validate all three.
I'm only banned on splatoon, but i've heard that some people got their console banned from Nintendo Services. I'm not sure what the error code is but if you need it i'll dig it up.
It's not that big of a deal. I just don't know what gets some people in more trouble than others.
But a way to make the server think you are a new console. Maybe if somehow during a system format we can get the Wii U to change all 3 identifications too trick the servers into thinking its a new console entirely ? All of this is ofc not impossible without iosu but maybe an external application or later iosu exploit can do so . Also similar to how the Wii changes a mac address when it is formatted . Instead of inject you change or get the Wii U to create if possible..
hacking is not an exact cience, it could take days or years, its just a matter of finding the corect stuff.
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