If something is marked Badatz Chatam Sofer or mehadrin, would it be considered Chalav Yisroel and Pas Yisroel?
Not necessarily. Anyone can mark something "mehadrin" and standards may differ.
You would need to ask the certifying authority or your local Rabbi. Those items that are chalav Yisroel that I have seen will have chalav Yisroel added to the label. Something could be marked mehadrin but still be Chalav Stam.