To scale your main character, you have to change the scale on that character. The origins all are global characters in the Divinity origins mod; their names start with S_Player_ (e.g. S_Player_RedPrince, S_Player_Fane, ...). The generic characters use S_Player_GenericOrigin and S_Player_GenericOrigin2/3/4. I'm not sure if their scale will be kept when they get transformed to the appropriate race and gender though.
Also keep in mind that the game maps have been made with the standard character sizes in mind. This means that if you increase the size, you may not be able to walk everywhere anymore. If you reduce it, you may be able to bypass certain obstacles.
I'm quite certain weapons won't scale with model size changes. I don't know about armor. It works if you scale NPCs, but equipment is handled differently for players and for NPCs.
So i opened up the divinity origins mods, now how to I select global characters? all I can see are the different maps.
