@Shlambate Drogos has been role played as a dark side inquisitor from the start. Are you looking to narrate him falling further to the dark side? We can do that by starting at 35 and going from there, if you want, calculating morality and conflict. Actually, the threshold is 30, so by the mechanics, you would not be a true dark sider until reaching 29.
Or you can just select a lower morality now, adjusting your ST and WT accordingly. Drogos is dark enough that I can envision him as already being there. But if you want to narrate him falling further, we can do that.