Has anyone ever though of pretending to be the perfect christian but behind closed doors a Pagan with ulterior motives? No one ever accuses radical christian leaders of being fakes, they just assume they are insane christians.
For example say I infiltrated the Jehovah's Witnesses... Gained their trust, and slowly try to take over the congregation. If I could replace one congregations 'elders' with false ministers perhaps I could slowly reprogram these self proclaimed sheep into my own followers, then send them out to subvert other congregations.
For conversation/theoretical sake, we could say that you could easily start dosing members with hallucinogens to break down their religious programming after you have their trust.
Then you could do what you will with your new flock! Either set them free or set them on a new agenda.
I put this in black magic because I am talking about destroying peoples faith in a religion and forcing your own will over theirs. But really I see it as trying to free people from a tyrannical cult. But then there is the aspect of converting them into ones own followers for power... Arguably not even a magical act, more of a manipulative one. But perhaps having a congregation could be useful for magic later?
You could also just let them stay hood winked and use your influence over the congregation to take advantage of them which would be pretty 'evil'.
But if you converted them to your own followers you could perhaps have a decent congregation to have perform rituals?
perhaps this is insane, but I have heard of people branching off of their church and starting a new one that they lead. But can one turn a bunch of christian sheep into a totally opposite religion?