If I was to send my wii to Nintendo, this is what I would do.
1- Make a nand backup
2- Have cios38-r17 installed
3- Run Priiloader Installer- Uninstall Priiloader
4- Run Nand Cleaner
5- Load MMM, Downgrade all ios to 4.1 - no patches, Delete all ios above 200, ensure all ios are not patched and official N ios of 4.1 version #
6- Install system menu 4.1
7- Run Hackmii installer, uninstall HBC, Bootmii, DVDx
8- Go to system settings, do a system format
9- Do a system update to 4.3
10- Do another system format
11- Cross your fingers and send it in
12- When it comes back, immediately make a nand backup and send it to TT. Install nothing but bootmii, then load it with the bootmii booter via disc exploit. They need these nand dumps, very important.
Note region changed wiis, or semi bricked wiis would have to take extra measures in returning the wii to the proper region and removing non region channels. Ensure the proper SN was in the setting.txt if you ever messed with that.
Even with that, softmods still may be detected. Who knows.