M’Intosh rests on asserted custom, not on any codified legal rule

Evidence

[T]he basis for the holding in M’Intosh: custom. Phrases like ‘understood by all,’ ‘exercised uniformly,’ and ‘universal recognition’ appeal to long-established practice, not to any specific constitutional, statutory, or common law rule. — Wikipedia contributors, Johnson v. McIntosh, 27

Categorization

• DEFINE: Clarifies what ‘custom’ means as a legal basis: practice claimed to be uniform and universally recognized rather than enacted.
• QUESTION: If the holding rests on custom, can it be overturned by showing the custom was never actually uniform or universal?