Section 2. Any city, except Boston, which shall adopt, in the manner hereinafter prescribed, one of the plans of government provided in this chapter shall thereafter be governed by the provisions thereof; and the inhabitants of such city shall continue to be a municipal corporation under the name existing at the time of such adoption, and shall have, exercise and enjoy all the rights, immunities, powers and privileges, and be subject to all the duties, liabilities and obligations provided for in this chapter, or otherwise pertaining to or incumbent upon said city as a municipal corporation; provided, however, that sections one hundred and twenty-eight to one hundred and thirty-four, inclusive, shall apply to all cities of one hundred and fifty thousand or more inhabitants, as enumerated by the most recent federal decennial census except any city which has adopted the Plan E method of city government.