Any pool mortgage loans insured must be on a "closed end" basis and no substitution of mortgage loans will be allowed; provided, however, if a loan in the pool is paid in full by the borrower, within thirty (30) days after inception of the insurance policy another loan may be substituted to replace the original loan; the substituted mortgage loan must be made subject to underwriting and review by the mortgage guaranty insurer and be found acceptable to the insurer prior to being added to the pool.
Cal. Code Regs. Tit. 10, § 2510.13