Okay, so in VX Ace, you could use
$game_self_switches[[map, event, 'self_switch']] = value
to manipulate an event's self switch. For example:
$game_self_switches[[@map_id, 7, 'C']] = true
would change event 7 on the current map's self switch "C" to "On," since in that code @map_id referenced...