You can get another event’s self switch with this in a script command:
get_others_self_switch("other_event_name", "A")
This will look for an event named other_event_name, and return whether its A self switch is on or not.
You can also change it with:
set_others_self_switch("other_event_name", "A", true)
Look for an event named other_event_name, and set its A self switch to ON.
Here’s an example on how to use them: