As a thief character, I reluctantly joined the dark brotherhood, but didn't really do much for them. I think I'm on my first 3 kill contracts. I went about a whole lot of other business, but I've decided I want to take down the dark brotherhood. I see that this is now impossible; is it possible to modify my save file so that all dark brotherhood stuff never happened, and I can do the whole "meet astrid in the cabin" thing again? I really don't want to lose my character/quests.

(this is on PC so that's not a problem)