4. School personnel. Employees of a school administrative unit who work the school year schedule may, upon written agreement between the employees and the school administrative unit, be paid for their work during the school year over 12 months or a shorter period, as provided in the written agreement. For purposes of this subsection, "written agreement" includes but is not limited to a collective bargaining agreement.

5. Change in rate of pay. Notwithstanding the provision of section 623 exempting salaried employees as defined in section 663, subsection 3, paragraph K, payment of wages or salary must be made at the rate previously established by the employer, except that the employer may decrease the rate of pay, effective the next working day, if the employer gives notice to all affected employees prior to the change. When an employer has temporarily increased an employee's wage rate to comply with the prevailing wage requirements of chapter 15; the federal Davis- Bacon Act, 40 United States Code, Section 276a et seq.; or other applicable federal or state law, an employer need not provide advance notice prior to returning the employee to the employee's regular wage rate, as long as the employer is in compliance with all posting and notice provisions of the applicable law. Changes of rates of pay made under a collective bargaining agreement are exempt from this requirement.