Changing world options mid-game

I know when you switch over to the “current world” tab in the options menu it gives you the warning that changing some of the settings can have bad effects. Primarily, I’m interested in upping the spawn rates to make my current game more interesting. Can that be done without wrecking my game?

Yes. But i assume you have static spawns, and that will only affect newly explored map zones, not hordes, for that you would have to edit savefile.