Use modmii to mod your wii from scratch as if it were a virgin, it will overwrite your old mods, no need to "unhack" the old stuff first. Also no harm in repeating steps.
Here's a slight deviation from the traditional modmii steps just for your specific case because to your problem with the system menu settings. We want modmii to have you install a NEW system menu, so whatever firmware you are currently on, pick something different, modmii will recommend you stay on 4.1 or 4.2 or 4.3, but make sure you choose to one of the other options.
Also,make sure u reinstall priiloader immediately after "installing wads" as per your custom modmii guide. By reinstalling a system menu you're overwriting and effectively uninstalling priiloader. So If you abandon the hbc without re-installing it first it will be absent and leaving you without extra protection, albeit perhaps only temporarily. Basically I'm saying don't get eager and skip steps or go off to check something else midway through the instructions.