No it's not possible to split or add new regions using this method as both require editing the pathfinding.esf. All you can do is add new campaign buildings where forts are located.
Khiva wasn't impassable as units could walk through this region. If it was impassable this method wouldn't work because you wouldn't be able to send a general into this region to build a fort.
Turning an unihabited (wilderness) region into an inhabited one has been possible for some time but the problem has always been editing the pathfinding.esf correctly. By using a method that doesn't involve editing the pathfinding.esf it's possible to avoid the main problem.