The Chofetz Chaim’s intent with the mishna berurah was that it should be used when one doesn’t have a Mesorah or minhagim, otherwise, on any particular shaila or issue. The CC did not intend mishna berurah to replace one’s established Mesorah or minhagim.
Indeed, there’s a famous story where the Chofetz Chaim himself practiced a certain halacha differently than he paskened in mishna berurah. When someone noticed and asked him why he’s doing differently than what the mishna berurah paskened, he replied that his minhag avos was different. If memory serves me correctly, I think he used a kos for Kiddush that was smaller than the shiur given in the mishna berurah. (Although, I might be mixing stories regarding the kiddish kos with Rav Moshe?)