Only against conditions written down in advance. Legitimate triggers are narrow: a territory change, a product line added or discontinued, an acquisition, or a clear arithmetic error in the plan. Document who approves a change, how much notice reps receive, and how in-flight deals are treated when terms shift. Never amend or cap a plan because a rep is earning more than expected, since that teaches the whole team that outperformance gets punished and the lesson persists for years. Give at least thirty days notice for any change.