OK, you've got your rep to Saintly and you've become a master in Light Magic. If you want to drop your rep to Notorious without slaughtering oodles of peasants, this is the way to do it.
First, donate a few times at a Temple of Baa. This will rapidly drop your rep to at most Average.
Next, sell all the bones you've been collecting. If you've given the game enough time for Bootleg Bay to have respawned and collected the bones from both spawnings, plus killing Longfang Witherhide and scavenging the bones from his lair, your rep should be well on the way down.
Following that, ask Wilbur Humphrey why Slicker Silvertongue won't let you access the Oracle, get the quest from him to do the Superior Temple of Baa, and finish touching the sequence of Baa Heads in there.
This should be enough to give you a Notorious rep, but if you need more, go and get healing from the Curator in Castle Kriegspire.
Don't do any of the "good" quests while you're doing these.