Canonum De Ius Positivum
Canons of Positive Law
II. Form
2.2 Form Creation and Change
Article 52 - Custom
Canon 1722 (link)
Whilst a Custom may have a long tradition, its lawfulness is dependent upon its consistency to body of Canon known as Astrum Iuris Divini Canonum in accordance with Pactum De Singularis Caelum.
Canon 1723 (link)
A Custom not considered lawful in accordance with these Canons, is therefore unlawful. A custom alone may not be assumed as an unwritten law.