What we are both trying to achieve, regardless of priorities, is this:
mrschwarz - without WAN cable connected the mobile will be set to Tethering On, then when mobile is connected to the router via USB the router will be set as “Connect to USB Tethering” automatically.
exitguyaus - as above. Also, if WAN cable is connected and internet working then when mobile is connected via USB it should override WAN cable until disconnected, at which time it will revert back to WAN cable if connected to active internet.