A family rule should be understandable without knowing which parent is in the better mood.

Rules that shift with mood teach children to read adults instead of learning the rule. The lesson becomes about timing and approach, which is a genuinely useful skill and an exhausting one for a child to have to develop at home. Consistency is not strictness. It is the thing that lets a child stop watching you.

Pick the two or three rules that actually matter in your house and make them the same on tired days. Say them plainly, and if you and another adult disagree, sort that out away from the children rather than in front of them. When you do make an exception, name it as an exception.