Those PIN_SR_xxx defines are for shift register. OSPi uses a shift register to drive many valves (including those on expansion boards) with just 4 GPIO pins. If you don’t use a shift register, you can use the GPIO station feature which is available in the current firmware. Specifically, the GPIO station is a station that’s drive directly by a GPIO pin, not through shift register. The PIN_FREE_LIST specifies free pins that can be used for GPIO stations.
What i suggest you do is to assign some dummy values to the PIN_SR_xxx’s, and make sure you don’t use these pins for anything else (because the firmware will toggle these pins assuming there is a shift register connected to these pins). Instead, you provide a list of free pins for PIN_FREE_LIST, and when you run the firmware, you can click on the gears icon next to each station name, to open the station attribute dialog, then go to ‘Advanced’ and choose ‘GPIO’ station, and select a free pin from the list. That way, you can bypass shift register and directly use GPIO to drive a station.