In my experience, revamps are notorious for scope changes. For project success, there must be a well-established scope change procedure so that changes can be dealt with in an orderly fashion yet with as little negative monetary or schedule impact to the project as possible. Examples of such changes would be sudden failure of an existing piece of equipment, an unplanned outage that must be taken advantage of or, conversely, a delay in the shutdown of some area of the plant.
The statement that: "Anything can be done and the impossible only requires more money!" is definitely a truism for revamp projects. Anyone attempting a revamp project must determine where the limit is and develop a plan to get there. Sequencing is perhaps the most critical because revamp means modification to an existing, operating plant and continued production has the highest priority. This means that revamp projects are marathons rather than sprints. The revamp team must maintain a vision of where they want to be when the project is finished and, ultimately, what constitutes project success.