You might look into MIDI devices, since there are programs to convert MIDI events to keystrokes.
For hardware, this seems kind of like what you’re looking for: https://www.sweetwater.com/store/detail/SamplePadPro--alesis.... There’s plenty of MIDI foot pedals as well. I don’t know about using the foot pedals as “modifiers” but I assume it’s possible.
For hardware, this seems kind of like what you’re looking for: https://www.sweetwater.com/store/detail/SamplePadPro--alesis.... There’s plenty of MIDI foot pedals as well. I don’t know about using the foot pedals as “modifiers” but I assume it’s possible.