As it has been stated before by many people here, using any manner of technical modification which includes but is not limited to:
- Simply running custom firmware on your switch
- installing NSPs/XCIs
- Cheating
- Loading various homebrews etc etc
So to put it simple, if nintendo detects any traces of said activity they could kick you off of any online activity. Furthermore this could potentially ban your cert thus making it impossible to download from nintendo's cdn servers such as system updates and game updates.
Therefore it is
NEVER recommended to go online on a hacked switch unless deemed safe to do so by our community.