Hi,
es_systems.cfg is in /etc/emulationstation/.
You can swap discs with your defined swap disc hotkey. Look in input settings in retroarch gui or in the configuration editor:
# Toggles eject for disks. Used for multiple-disk content. input_disk_eject_toggle = # Cycles through disk images. Use after ejecting. # Complete by toggling eject again. input_disk_next =Put your prefered button after the = . Ingame press your hotkey button and your button eject and swap discs.