Except as otherwise provided in chapter 15-39.2, the laws pertaining to the teachers’ fund for retirement, as contained in chapter 15-39.1, apply to teachers, superintendents, assistant superintendents, principals, assistant principals, special teachers, supervisors of instruction and other supervisors, presidents, deans, school librarians, and registrars employed by any state institution under the supervision and control of the state board of higher education and the commissioner of higher education, only in the form and substance as chapter 15-39 existed as of July 1, 1967, and all such persons have only such rights, benefits, and privileges as provided in chapter 15-39 as it existed on July 1, 1967. Such persons are responsible or liable for only those costs or assessments provided for in chapter 15-39 as such laws and chapter existed on July 1, 1967. The state board of higher education or any institution under the supervision or control of the state board of higher education is not liable for any costs, assessments, or payments under the provisions of chapter 15-39 in excess of that provided or required under the provisions of chapter 15-39 as such laws and chapter existed on July 1, 1967. It is hereby declared to be the intent of the legislative assembly to freeze the rights, benefits, privileges, assessments, payments, and obligations of the persons, offices, and institutions specified in this section to those rights, benefits, privileges, assessments, payments, and obligations as they existed under the provisions of chapter 15-39 as such laws and chapter existed in form and substance as of July 1, 1967, and that all legislative enactments subsequent to such date do not affect or apply to those persons, offices, and institutions specified in this section or their rights, benefits, privileges, assessments, payments, and obligations as fixed by this section.