There's a "Betrays on Arrival" option in escort objectives that's supposed to make them turn on you when you get to the exit. I've never used it myself, so I can't say how well it works.
That's the only way of going about it as far as I know.
It works well, except that sometimes they don't attack until attacked (which I assume is bugginess, rather than intended, as sometimes they do go right after you).
Dec out.
IS there a way to have allies that work with you up until a certain point or after an objective is accomplished and then turn on you? I have tried to do a search for this and look through the MA system online but can't find or see a way.
Is there some trick to do this kind of thing or can it simply just not be done.
Thanks.
Deus