Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - Game Master Saving campaign in progress and adding stuff.

Seter from Larian provided an unofficial way to do that. But warned to make at least a backup because of possible level data corruption
See here: http://larian.com/forums/ubbthreads.php?ubb=showflat&Main=77440&Number=628895#Post628895