A life insurance company may increase the amount of its reserve liabilities by changing the basis of computation as provided in Insurance Code §425.067, concerning Optional Reserve Computations. The insurer may establish a higher reserving basis by reporting an increase in reserve in Exhibit 5A of its annual statement. Thereafter the insurer must continue to report on the higher basis. An insurer may, with the approval of the Texas Department of Insurance, as provided in Insurance Code §425.067, adopt a lower standard of valuation, but not lower than the minimum standard provided in Insurance Code §425.053, concerning Annual Valuation of Reserves for Policies and Contracts Issued Before Operative Date of Valuation Manual.