Except as provided in sections 77.042 to 77.048, the mayor and city council of any third class city and the mayor and board of aldermen of any fourth class city which adopts the city administrator form of government shall retain all the powers given to it by the laws applying to the city before the city administrator form of government was adopted, and all laws governing the city under its prior form of government and not inconsistent with the provisions of sections 77.042 to 77.048 shall apply to and govern the city after it adopts this form of government. All bylaws, ordinances, and resolutions lawfully passed and in force at the time the city administrator form of government is adopted shall remain in force until repealed or altered by the council or board of aldermen.