I've just finished chapter 2 in the original NWN1 campaign and I realized I had forgotten to talk to Aarin Gend and listen to his story. I have no saves before the mage's tower, and he won't talk to me about anything else than my mission. Is there any way to use the cheat console to move back to Chapter 2, to make him tell the story, or to make him think he actually told it?

Are you trying to romance him? This makes a difference.

Just finish the quest! But I found a way. Start chapter 3, save the character, start a new game from chapter 2, finish his story, save the character and once again start a new game from chapter 3 :) No cheats involved!

That works in this case!