Saw this question in Oliver Lehmann 75 questions.

What is a constructive change?

1. A change request that helps improving the project and its product, service or result and is discussed generally in a friendly style.

2. A direction by the buyer or an action taken by the seller that the other party considers an undocumented change to the contract.

3. A field change or ad-hoc change mandated by the project customer in a public construction project.