A similar button mapping can be made for PD, but the switching would happen by killing existing PD instance and starting a new one, with a different patch. See here: Adding more button clicks
You could disable the pisound-btn functionality altogether (sudo systemctl disable pisound-btn), and detect Pisound’s button clicks by somehow reading the Raspberry Pi’s GPIO17 pin - when it goes low, the button is pushed down. I don’t know how to do it in PD, but I’m sure there are convenient ways to access it. 