Can a city be compelled by court decree to agree to and execute an amendment to its contract?

In order to sustain the power of the superior court to order the city to grant to respondent an increased rate it is necessary for respondent to find authority to the effect that the city may be compelled by court decree to agree to and execute an amendment to its contract. Counsel have not cited or hinted at any such authority and we know of none. The case of City of Detroit v. Detroit Citizens' Street R. Co., supra, and other cited authorities, plainly indicate the contrary. 'Were the municipalities * * * in the granting of the franchises involved in these cases, expressly vested at the time of the granting thereof with unlimited authority to contract with the grantee of such franchises on the subject of fixing the rates which might be charged for the services rendered the public thereunder during the whole of the franchise periods?