Rob
Your response is based I believe on the assumption that it has been proven that the contractor has not complied with a constraint contained in the WI.
If this is not correct, and it is purely the rectification of a defect, am I right to assume that all consequential costs, such as formwork extended hire etc would be deemed to be Defined Costs and not subject to disallowance.
If you have been instructed to do something by the Project Manager then under clause 27.3 you are obliged to follow that instruction. If this is something that they may perceive to be a defect, it is up to you to notify that this instruction is a compensation event - stating why within clause 60.1 it is one. Providing they agree it is one, they then request a quotation and you will assess that in terms of defined cost like you have highlighted.
If the Project Manager responds to your notification that they do not agree it is one - you have no contractual recourse other than formal adjudication to over turn that decision. When you initially notify it is a CE you need to make it very clear why it is one with all the evidence you have - i.e. put the Project Manager in a position where they can’t say it is not a compensation event (unless of course it isn’t!)