If you have a rule that your child must go to bed at 9 PM every night, and one night they ask permission to stay up late, you need to be careful about how you grant that permission. You must make it clear that it is an exception and that the rule hasn’t changed. Otherwise your child will come back with the same request night after night.
At work, things are different. As a leader, you can’t allow employees to break a policy, not even once. Or allow employees to ignore one policy but follow the others. Once you open the door to breaking a policy, you have lost all power to enforce any of them.
If a policy must be broken or ignored, then a leader ought instead to revise it or delete it.