Say the advance payment repayment is pegged at $128 000 per month, can the Project Manager increase this figure to say $220000 and this is done without consultation with the contractor.
Assuming you have Secondary Option X14 and the amount to be re-paid in instalments is stated in the Contract Data as $128,000 per month (assumed this is your assessment interval), then the Project Manager is obliged to deduct the amount stated. As this is information stated in the Contract Data, then it can only be changed by a Deed of Variation between the parties to the contract.
Similarly, the Project Manager could not decide, for no particular reason other than his own opinion, to increase the retention percentage from 3% to 5%, if it is stated in the Contract Data to be 3%.
No ! Nothing in the contract allows the PM to do this without a supplementary agreement being agreed in accordance with clause 12.3.