Not exactly sure if this has already been mentioned, or if it shouldn't be mentioned (in which case mods can freely change this post to reflect so), but there's a very easy method to change routes way into the game, without restarting.
Simply make a save, and then go to a save editor, and search for route_romance and route_mb . Whichever route you're currently on will have 1 , if it's a 1/0 situation, meaning if on romance, it's route_romance 1/0 1 . Just switch them around, so whatever is 1 , make it 0 and whatever is 0, make it 1. Then suddenly, all the routes you changed have switched.
'Course, this doesn't apply retroactively, so you can't get old one-time events with this new route, unless you've got more saves before those, but it's pretty nice if you want repeatable events.