Contracts entered into prior to the date the provider receives the certificate of authority are valid and binding for those providers offering or providing continuing care on January 1, 1989; except that a resident or a prospective resident who has signed a contract prior to that date may request that his contract with the provider be changed to conform with the provisions of this chapter. However, any changes made to such contracts after the date when rules adopted by the commissioner in accordance with N.H. Rev. Stat. § 420-D:17 take effect shall conform to all provisions of this chapter and such rules.