Yes, Please, Avoid Decrees
My best IT manager was the one who had the ability to "read the situation" and adjust any policy or procedures accordingly. "Adjust" - not violate or ignore.
She was also the one who's motto was "Sometimes, it's better to ask forgiveness instead of permission." Plenty of managers are terrified to do this - they operate out of fear - fear of getting in trouble, being accountable, or making the wrong decision. But a good manager will know when to play this card - a bad one, well, won't.
My own personal motto is, "No one ever did anything amazing just by following the rules." Just don't tell that to my boss...