Am I able to modify Zerynth to support a SparkFun Pro nRF52840?
Unfortunately, I don’t think you can modify Zerynth to support that board, because the Virtual Machine (firmware) is usually made for a specific board.
Surely it is only changing the PIN out allocations?
at the moment creating custom Virtual Machines for board with different pinouts is available only for ESP32-based boards. Though we are planning to add this kind of support also to other architectures, I am unable to give you a precise date.
Anyway, let me know if you plan to develop a commercial product and need to prototype on that board.