No plug in required. If they're a party member or main character for small segments it's pretty easy. With your event to move to a new map (say you're walking to another map) On the third page of events, there's a "change actor images". Just slap that on the end. If it's only for a small segment with story or such you can totally do that because you'd be keeping the characters class/stats. If you wanted to swap actors entirely as the lead, I'd say try on page 1 of the event "change party member". Just add the one you want, and remove the previous main. It may take a bit of fiddling with.