Modifications of Contracts.
   Section 37. When it becomes necessary in the opinion of the village manager, in the prosecution of any work or improvement under contract, to make alterations or modifications in such contract, such modifications or alterations, if made, shall be of no effect until the price to be paid for the work and material or both, under the altered or modified contract, has been agreed upon in writing and signed by the contractor and by the village manager and approved by the Village Commission.