No there is no where in the contract that expressly allows them to insist you change your activity schedule. The Contractor can propose to revise it under 54.2 and the Project Manager has to accept/not accept for reasons under 54.3. there is no where that says the Project Manager can insist they change it. Ask them to show you in the contract where it allows them to do this? (If all they have is "surely in a spirit of mutual trust and cooperation" then they really are clutching at straws.)
Having said that, by agreement you can. If they are asking you to split the amounts so that some payment is reliant on you getting acceptance rather than you submitting (rubbish!) then you can kind of see their point. Even still - contractually they cant force you to. This would be one that might be worth doing just to show willing and for relationships - with you showing some of the money reliant on acceptance (but you decide how much).
Having said that, by agreement you can. If they are asking you to split the amounts so that some payment is reliant on you getting acceptance rather than you submitting (rubbish!) then you can kind of see their point. Even still - contractually they cant force you to. This would be one that might be worth doing just to show willing and for relationships - with you showing some of the money reliant on acceptance (but you decide how much).