Just have the Norwegians know that the ships are invading Germans and not British, with alert defences. It would be the doom of Kriegsmarine. Hipper along with 3 destroyers could have been hammered by coastal artillery while full of mountain troops. In OTl it was thought to be a British warship and passed unmolested. Between the coastal defences ( as the Germans needed to seize ports and not just land somewhere) and the RN, the surface Kriegsmarine fleet would almost seize to exist.