you’re less likely to get any help with that from aloshi than you would from the retropie dev’s as he hasn’t touched his code in at least 6 months.
As it stands the only two ways I can think of accomplishing your task is to basically simulate key presses that take you into the supernintendo menu in emulationstation as it boots, or script it to boot into the rgui with the snes core loaded- but both are pretty singular use cases that would have to be custom scripted for your needs. There may be other ways as well, I’m not the most skilled at coding.
perhaps in the future if aloshi ever picks up development again, it may be integrated as an option in emulationstation but yeah retropie wouldn’t be messing with that code.