According your guide all services qubes will work without selinux or apparmor.
I prefer to think twice before drop extra layer of protection from sys-usb and sys-net, better to clean up xfce\gnome template with already function apparmor\selinux from unnecessary content.
Navigate to start menu, Qubes tools → Template switcher, use it to switch templates.
As more advanced user you can perform same process with CLI in fail save way for sys-usb: