I have not found a way yet to play EA again. I've legit e-mailed Larian asking for it too.

I can only guess as to why there was such a drastic change. Because one day (in EA) I'm playing the last EA patched version and the following day on release... a bunch of stuff blinked out of existence. My guess, is they ran out of time. Various zones (like Upper Baldur’s Gate) are just removed (said zone is just a stage now). Various story lines are incomplete. There's story threads that stop cold (there's supposed to be more Hags if the various letters/notes/and NPC conversations are to be believed). The whole end sequence were the capture dragon shows up... how they got that dragon is never shown... etc. So, that's my guess, they had more ambition than time.

Oh another idea that wasn't completed. Karlach (the last character added/worked on) is the only origin character you play that you can hear the inner thoughts/monolog. Everyone else is silent.