Notwithstanding any other provision of this part, the board may adopt a funding period of 30 years to amortize unfunded accrued actuarial obligations for current and prior service for the purpose of determining employer contribution rates for contracting agencies and school employers. The board shall approve new amortization periods based upon requests from contracting agencies or school employers that can demonstrate a financial necessity. The board may deny a request when the request would subject the fund to an unsound financial risk. This section shall not affect the current procedure for setting the school employer rate. The board shall continue to treat the school category as a total experience pool with no requirement to establish separate rates for a school

district subject to this section.