Generally u should avoid uninstalling wads, if u uninstall the wrong one u can brick yourself. Some yawmm mod will mostly prevent u from doing something catastrophic, but wii mod lite will allow u to uninstall crucial files, like the system menu or system menu IOS.
If u aren't sure, it's always safer to uninstall channels from the wii's official data management settings menu
Edit: I forgot to mention u can almost always overwrite wads with new ones just by installing them so long as they share the same ID, no need to uninstall anything
Edit2: u can recover from bannerbricks and theme bricks with just priiloader, but other wads may render priiloader useless (I. E. If u stub your system menu IOS or install a new system menu without reinstalling priiloader afterwards). For the title it's clear to those of us that know this stuff that u weren't referring to system menu wads and ios wads, so this info is more for others that may happen to read this in the future