I want to sell my Nintendo Switch and account, but I have concerns with the two-step authentication (I know that selling accounts is not legal). Can I change the authentication email address or not?
Why do you want to sell an account?
Because there are games on it and you can only play them with your account.
I know that selling accounts is not legal
It is legal! You won't be arrested for that! The correct word is "forbidden" or "not allowed". It would be illegal if this violated a law, but the sale of accounts only violates Nintendo's terms and conditions! That's a difference!