You cannot configure or add to the cases in ARPlaneAnchor.Classification.
If you would like to see smaller vertical planes with "typical size and appearance" of a wall classified as walls, please file an enhancement request using the bug reporting tool at https://developer.apple.com/bug-reporting/
What I actually archieve to do is detect a wheel.
It is detected as vertical plane but not limited to it's actual size.
But thanks for your answer.
I will stick with my combined CoreML solution.