The municipal corporation may enter into any agreements and contracts necessary to carry out the powers and duties prescribed by RCW 54.04.130 and 54.04.140, but nothing in RCW 54.04.130 through 54.04.160 shall be so construed as requiring without consent the modification of the obligation of any contract or as requiring any third party to modify the rights, privileges or obligations acquired or incurred under a prior agreement.