One more thing to add about editing the systemlist.xml in /recalbox/share/system/.emulationstation/, if you just want to add additional system(s) you don't need any of the other system information in the file, just the new system(s) info you want to add. For example I added a new system for all the trackball games on my arcade, I kept the mame systemlist information in the file and deleted the rest of the info in the file, I then edited the mame system info by changing the fullname, path, and theme. I also changed a few characters in the uuid number/letter chain to make it unique. I'm pretty sure this is also a necessary thing you need to do.
