BEHAVIOUR 01 / 03
Change staffing and scope in the Project Plan, and watch the margin move.
When a senior comes off the project, the row stays as an open role, still costed at its standard cost rate. Hold it open, take a substitute at lower cost or scale back the allocation. Margin recalculates with each change, so you see what losing the senior costs and what a mid-level brings back.
The Project Plan: a row for each person or role, with charge rate and CM% against target, and a change request waiting to be signed.