Can. 26 Unless it has been specifically approved by the competent legislator, a custom which is contrary to the canon law currently in force, or is apart from the canon law, acquires the force of law only when it has been lawfully observed for a period of thirty continuous and complete years. Only a centennial or immemorial custom can prevail over a canonical law which carries a clause forbidding future customs.
Can. 28 Without prejudice to the provisions of can. 5, a custom, whether contrary to or
apart from the law, is revoked by a contrary custom or law. But unless the law makes
express mention of them, it does not revoke centennial or immemorial customs, nor does a
universal law revoke particular customs.