Dear Avira,
Are you saying that proving ‘pig is not trief’ is megalah panim et alia? I think that would be correct. But I think that if we are wrong on this, that would not be a problem. It’s a mistake with no implications beyond what we would actually be wrong about. Meaning, someone would post ‘proofs’ that pig is kosher, and you and I would say that he is a megaleh et cetra, and Eliyahu would say he is not [Shrug. It’s a hypothetical anyways. Even today the mods won’t let it.] I think at least we would not be megaleh panim batorah, because nobody is going to eat pig or not based on how we label this wrongheaded poster. Since we weren’t advising anyone to do an issur, we were nothing other than mistaken. and we get rewarded both for stopping people from eating pig. And Limud HaTorah, eve though we erred. That’s my take. Would you say that we would be in the category of megaleh panim for wrongly saying that the poster is in said category?
PS Which of the above statements would be heresy in the reverse? Not just wrong. Actual heresy.