Assessment of Compensation Event - NEC3 Option B

In an instance where the Project Manager (PM) has proposed to assess a Compensation Event quotation, based on the prices in the Bill of Quantities and the Contractor has agreed to this, can the PM later change its mind and revert to an assessment using Defined Costs?

Yes, they can, but doing that has consequences. The PM would have changed a decision that they had already communicated, so a new compensation event arises under 60.1(8).