I have a very complicated situation, so I'll try to be fast. In order to correct the things my last one got wrong, I plan on making a new NNID, but I found out that the purchases I made are linked to the account and will be deleted along with the account. I know Nintendo Support says something about formatting, but they don't go in to detail, so I was wondering if anyone could tell me about my options. Could I sign in and out to different accounts and have games on both accounts, or is there any way for me to save my old games (don't care about save data) and put them on a new NNID?
Strictly speaking, there's no way to transfer purchases from one NNID to another.
Additionally, you will need to format the system in order to un-link it from the existing NNID. This will remove any games from the system.
Therefore it will not be possible to retain your existing games if you decide to create a new NNID.