Any company owning, leasing, or operating street railroads, suburban railroads, or interurban railroads in this state shall, by virtue of this Code section, and without any action on the part of the commission, have the right and privilege of substituting what are known as trackless trolleys on any part or line of its railroad system, provided that consent thereto is obtained from each municipality affected by any such proposed substitution, which consent on the part of any municipality shall not be construed to impair any valid existing contract or ordinance contract now in existence between any such municipality and any such company; provided, further, that nothing in this Code section shall be construed to impair any valid existing contract or ordinance contract now in existence between any such municipality and any such company; provided, further, that the commission shall not have the power or authority to increase or authorize the increase of, in regard to such substituted service, fares which have been fixed prior to March 30, 1937, by contract or ordinance contract on the line or lines on which such trackless trolleys may be so substituted, which fares shall in all respects appertain and apply to such substituted service when thus inaugurated.