I think it would be better off letting the primary fermentation finish and the yeast clean it up followed by sweetening. I just did a cider batch and tasted it right after primary ferm was done. There was a really unpleasant tingly, almost burning sensation on the tongue. Waited one more week then tasted again and it was all gone. Maybe it improved by sitting on the yeast longer, maybe not, either way I wouldn't have wanted it in the finished product.
