Minimenu includes some easy to use options to recategorize applications (it creates/edits ovr files as needed, without you knowing how it works.) If you're using xfce and not minimenu, you could just switch to minimenu to do the recategorization, and then go back to and keep using xfce.. the changes still apply. (the ovr files are system wide, not related to xfce or minimenu or other launchers.)
ie: minimenu lets you create new categories/subcategories too, though xfce will push apps in those to Other
jeff