@antoine.pasde2 The simple answer is that I could, but that would also potentially increase the runtime managing both interfaces. So yeah, good point I might not even bother.
@Farabide I fully intend on continuing to expand the WIKI. This project is consuming a lot of my time right now, but I plan on detailing a full how to along with the release of these PCBs. The WIKI of course will not be written in any way that you would need to use them, but from my experience, I think it will make this whole process much more simple. This is still very much a DIY endeavor.
TLDR; you would use a digital input pin with a toggle switch that can set a flag for use with conditionals in the program to trip either initializing a serial interface, or an interface with USB. Any changes would need a reset of the device (unplug and plug back in works fine).