I'm not aware of one. Personally, I use unassisted 'rule of drama' like Nicos and Zhayne. But here's a rough idea you can develop if your table needs a system.
The GM can assign the potential convert Devotion Points (faith) and Principle Points (alignment) - or whatever naming system works for you. They'd work a bit like hit points: the missionary has to degrade the target's store of Devotion and Principle before conversion is possible. I'd probably suggest allowing one Diplomacy check per day (either against a Hard DC or made as an opposed roll vs. the subject's Knowledge (religion)) to take away 1-2 points at a time... while actually demonstrating the benefits of the faith/alignment would be worth more than words. The potential convert can regain Devotion or Principle if subjected to contrary opinions or witness to contradictions or failures of your philosophy. That's why cults build compounds.
Obviously, some subjects would have more Devotion and Principle than others. Practically all religiously inclined paladins, the most devoted priests, and other extremely pious characters could have the max of, oh, say 100 Devotion pts, and you have to whittle them all down while trying to avoid having anything counteract your efforts. Ordinary 'holy days only' followers might only have 20 or 30 points. Reaching 0 would produce an apathetic theist with no real beliefs: at that point you need to add Devotion before they've really converted. (An anti-theist should not be assumed to have 0 Devotion: they still have Devotion, just not to a god.)
Principle would work similarly, except that some beings would have "-" in Principle just as some have "-" in Constitution. Animals, mindless creatures, aligned outsiders and undead are 'stuck' and shall not be swayed. Note that while 0 Principle points would probably mean a temporary alignment of True Neutral, folks who are True Neutral could have as much or as little Principle as anybody else.
If you break down one but not the other, you've got an apostate (old faith, new alignment) who isn't on your side yet but won't be accepted by prior allies - or a hypocrite (new faith, old alignment) who pays lip service to your faith without actually understanding the moral viewpoint required. Obviously neither is desirable... except to the GM, who will love it.
