No ordinance adopted by an electoral vote can be replaced or amended except by an electoral vote. But an ordinance to repeal or amend any such ordinance may, by resolution of the city commission, be submitted to an electoral vote at any regular election or at any special municipal election called for some other purpose, provided notice of the intention so to do be published by the city commission not more than sixty (60) nor less than thirty (30) days prior to such election, in the manner required for the publication of ordinances. If an amendment is so proposed, such notice shall contain the proposed amendment in full. Such submission shall be in the same manner, and the vote shall have the same effect, as in cases of ordinances submitted to an election by popular petition. Such ordinance to be voted upon shall be published in the manner provided by Section 20 hereof.