Can KLANG:app listen to custom OSC messages on a different port than 9111?

Yes, you can configure Custom OSC Receive Ports in KLANG:app:

Go to KLANG:app (5.6.7+ required) > CONFIG > INFO > Set Menu > Custom OSC Receive Port > and enter an additional port KLANG:app should listen on for incoming OSC messages, e.g. 9112.