A hex edit can also enable 4 player co-op in the main game, but that wouldn't have the extra character creation (the 3rd and 4th players would need to control companions / henchmen).
Open the '..\Divinity - Original Sin\Data\Main.pak' file in a hex editor, search for the term "NumPlayers" (with the quotes), and change the 2 to a 4. The ASCII side of the hex editor will show the following:
<attribute id="NumPlayers" value="2" type="1" />
If you (or the hex editor) make a backup of the original file, move it to another folder; having extra/backup pak files, even renamed with a different extension, in that folder can cause the game to crash on startup.
You may be able to use the 4 player mod to start the game, and then save and switch the meta.lsb file in the save to enable the other mod (using the hex edit to continue 4 player co-op). See
here for details on that procedure (though a slightly different situation).
