is it possible to update the contract value from amount spent on PO...?

Dear Gurus,

I have a business scenario in SAP MM, where I need your expert advice.

I have a contract say, worth of 1000 USD. against which I have created 9 purchase orders of 100 USD.

But I have done service entry of 50 USD only for the each PO. & I am not expecting any more . So the actual money spent is only 450 USD. But the Total PO issued is for 900 USD.

Here with the present configuration , the remaining money in the contract is showing only 100 USD ie I cant create any PR for more than 100 USD.

Even though I didn't actually spent , I am losing the amount of 450 USD from the contract.

Is there any way to resolve this so that the remaining contract value will take the actual spent value as reference.