When this mayor-council form of government becomes applicable to a city, said city shall continue as a municipal corporation, within the corporate limits as now established and as may hereafter be fixed in the manner prescribed by law, subject to all duties and obligations then pertaining to or incumbent upon it as a municipal corporation and shall continue to enjoy all the rights, immunities, powers and franchises then enjoyed by it, as well as those that may thereafter or hereinafter be granted to it.