Subject to other limitation in chapter 7, title 41, Idaho Code, an insurer shall not invest or have invested at any one time more than sixty-five percent (65%) of its assets in investments described in sections 41-721 and 41-728, Idaho Code. Any insurer which, on July 1, 2003, has in excess of sixty-five percent (65%) of its assets so invested shall not make any further such investments while the excess exists. The limitations prescribed in this section shall not apply to mortgage-backed securities rated one or two by the securities valuation office (SVO) of the national association of insurance commissioners or to mortgage-backed securities which qualify as provisionally exempt from filing with the SVO.