Your NNID (if you have one) will not be affected by this guide. Consoles with a region of KOR, CHN, or TWN do not have NNID functionality to begin with and are thus unaffected.
+ +Following this guide alone should not result in data loss (saves, digital games, etc), but SD card corruption is always a possibility. You should make a backup of your SD card contents if you have important data.