MIDI Device Manager program number formula

There’s a one-off problem, changing the slider to say 71 selects 72 on the external device. How can I change the MIDI Device Manager send the selected number -1? I see there’s a formula field in the program change transmission settings, I tried x-1, but that doesn’t work.

Another question: How do I delete some of the superfluous, godforsaken parameters from this view?