Are Nintendo Network IDs created automatically?

No. Unlike friend codes used on Nintendo 3DS, Nintendo Network IDs are not created automatically.

I accidentally chose the wrong Nintendo Network ID. How can I change it?

Once you have chosen your Nintendo Network ID, it is not possible to change it.

I accidentally set the wrong date of birth. How can I change it?

Once you have entered your date of birth it is not possible to change it.

If I use the same Nintendo Network ID on my Wii U and Nintendo 3DS, what should I do if I wish to give one system away?

Before giving away a system with a registered Nintendo Network ID, please contact the Nintendo Service Centre, who will be happy to help.