After this charter takes effect local improvements commenced prior thereto shall be completed and assessment may be levied and securities issued for the financing thereof as prescribed by the law (or charter provisions) applicable thereto. The council may prepare and adopt a comprehensive ordinance prescribing the procedure which shall be followed thereafter in making all local improvements and levying assessments therefor. Such ordinance shall supersede all other provisions of the law on the same subject and may be amended only by an affirmative vote of a majority of all the members of the council. In the absence of such ordinance all local improvements may be made and assessments levied therefor as prescribed by any applicable law.