No, I meant that if the ruler being attacked by the Orthodox ruler is not Christian, but a county in the duchy being fought for is Orthodox. Basically, you'd be waging a holy war to free the Orthodox Christians suffering under non-Christian rule. If you loose land to an Invasion or something, it could be used to push back, but it couldn't be used for expansion of the realm.
Hmm. I see. It's not a bad idea - granted, it would probably encourage a little bit of ERE blobbing, though not too much - and frankly it could apply for most of the religious groups anyways. Meneth has already added a religious reconquest CB in Project Balance (so it's there in PB+VIET), but I wouldn't be against adding something like that for the vanilla version... but I'll have to think about it
But anyhow, for now, as al3xytp said, there is the customization option.