Create a forwarder dol to apps/yawmme/boot.dol or whatever wad manager / tool u need. U can use modmii to do this, from modmii classic's main menu, enter A then F the build a V14 forwarder dol
Save the forwarder dol to sd root, install dol as file on preloader, launch installed file (make sure it exists on device)
If u need other homebrew either create a new forwarder dol or just save what u need to the location of the one installed
From there u can reinstall your system menu wad for your region, make sure u have the corresponding system menu ios installed if u are changing version #s, and u should use yawmme and not a dif wad manager as it will allow u to retain priiloader during this process, other wad managers will wipe out priiloader when installing a new system menu, and preloader is your lifeline right now so u don't want to risk losing/updating it until all other issues are resolved