Make a change you can take back

The value of a reversible change is that a wrong guess costs a rollback rather than an outage. Before a change touches a live system, decide what taking it back would involve.

Write the way back first

Before the change, name the state you are leaving and the step that returns to it. A change with no way back turns one bad decision into a long incident.

Change one thing at a time

A live system has several moving parts. Changing the secret and the prompt and the version together means a fault cannot be traced to any one of them. Move one, watch a full turn, then move the next.

def can_revert(change):
    return change.previous is not None

Let the turn finish

Applying a change mid turn leaves the system holding a fragment of the old and the new. Wait for the turn to end, apply the change, and confirm the next turn completes before the old path is retired.