to uninstall yumex, go:
Now if you are worried about messing up on installing YDL itself, you will NOT affect the PS3 Game OS, it is safely protected by the PS3 hypervisor and can not be addressed from the Other OS system, no matter what you do. You do not need to uninstall YDL, you can just reformat the harddrive if you wish to start fresh. Reformatting only erases game saves and pics/music in the Game OS, not the game system itself. And of course you can back up your game saves etc. to a USB drive or whatever prior to a reformat.