I must admit that I'm unsure.
Normally - when starting a new NwN game after installing either SoU and/or HotU you get access to the new feats, classes and skills. You don't however get access to the new henchmen AI/Inventory stuff. So no organising henchmen inventory in the original NwN (withouth community made modifications).
However - I'm unsure how the game would react to an existing savegame. Rationally - I'd suspect you could continue to play your exisiting save games without problems, and that you would now get access to the additional feats, skills and classes. However, I've never tested this personally, so I can't say for sure.
The reason I think this, is because the game is so modular, that each chapter is a differnet module in its own, and thus actually an individual game in the game as a whole. Therefore I dont see problems with it......
But as I said - I haven't tried it myself.
If you do try it, remember to back up your save games, so you always can revert to the old setting if things dosen't go as planned. Your experience with this would actually be appreciated, so if you try it, please come back and tell how it went
Linear Mode
