During the winter I carry a "standard" black zip up jacket from Columbia for layovers as well as the double breasted blazer. Once we're at the aircraft, if the conditions are such that I don't think the blazer is going to cut it for the walk around, I announce loud enough for the CVR that I'm going with "non standard outerwear for the walk around in the interest of comfort and safety" as I pull my layover jacket from my bag. Never once have I gotten push back from a CA or LCA. Usually the response is just a chuckle or a "do what you gotta do!"