Nothing in sections 469.004 to 469.008 shall alter or impair the powers and obligations of city housing and redevelopment authorities created under Minnesota Statutes 1969, chapter 462, prior to June 8, 1971, nor shall the area of operation of such city authority be included within the area of operation of a county or multicounty authority created pursuant to sections 469.004 to 469.008. With the consent of the board of commissioners of a city authority and the governing body of the city, a city authority may become a part of a county or multicounty authority upon assumption by the authority of the obligations of the city authority.