You can, but really the best time to cut back hibiscus is spring. This article will help with that: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/tips-for-pruning-hibiscus-plants-when-to-prune-hibiscus.htm

As for winter protection, a good layer of mulch should be plenty in your area, as long as what you have is a hardy variety and not tropical.