Is the Project Manager permitted to impose acceleration, on the Contractor.
Project Manager can instruct the Contractor to provide a quotation to accelerate, but not instruct the Contractor to accelerate. Acceleration should be by agreement not enforced and contractually (without Z clauses) can not be imposed. The Contractor gives their quote to accelerate and the Project Manager either accepts or does not accept. If they accept the Completion Date comes forward by the agreed amount and the amount in the quotation is paid, otherwise there is no change to Completion Date or the Prices.
It is unlikely that an amendment allowing instructed acceleration would be legally enforceable, or rather, if it were delay damages would probably be unenforceable due to the uncertainty the Contractor has on his Compeltion Date