[Greg McKaskle]

I didn't say this wasn't technically possible. I don't really advise doing it though.
It is sort of like you have a gasoline car and you are deciding to add a diesel engine to it. You aren't swapping to diesel, just adding the second engine in because you have it and half the mechanics are gas experienced and half diesel experiences.

If you are set on using both, the four slot has enough memory to run both, and you can run them side-by-side and communicate using network protocols or possibly even network tables. But you need to pick which one does the WPILib FPGA control. It will not work to do it in both.

Greg McKaskle