So, I've done alot of them, and just now Vingalmo sent me to turn Cairine in the Markarth Warrens into a vampire. The problem is I've received and completed thie exact mission before. I can't turn her into a vampire again, her dialogue is all vampirism now and it won't let me feed on her after seducing her. Anyone know of anyways to reset this? I can't reload a save, I'm hours in . I'm going to try killing her to fail the quest.

You have kill her to fail the quest. Hope that you dont get the bug where they will say "Go speak to Vingalmo" and then he doesnt have any quest options. I have had that one since the Beta

Killing her solved it. I'll be sure to save before speaking to them for radiant quests now, thanks for the heads up.