Ah sorry. I do not know.. calling Nintendo would be the only solution I can think of, but since you are banned..
There is no way to unlink the NNID server-side AFAIK, other than calling Nintendo, and like I said, since you're banned, they might not be kind.
For the ban, it would seem it is "confirmed" to be permanent, but we do not know for SURE yet.
Oh you can contact Nintendo of Japan? I don't think it matters if you reply or not... you're already on a blacklist if you are banned. x:
EDIT : Thread was posted