I did some searching about reset the Atari after playing game back to menu. Some say its impossible without power cycle. Interesting PlusCart (probably Unocart) somehow have it working. You need to press joystick to right and Game Reset switch. Not sure if anyone has looked into how they are able to do it since its open source.
Either way its amazing tech for the Atari.
I know how they do it on Pluscart, as I discussed it when the idea was proposed. It's possible for Harmony too (using the same method as pluscart) for most games, it just hasn't been done yet as I have many other active projects. I plan to expand on the capability and allow more than just game resets back to the menu.