A depository may effect a plus substitution of securities at any time; provided, however, that no agent of depository shall release a security from a security pool pursuant to such a substitution unless a duly authorized officer thereof first endorses upon or attaches to the documents of substitution a certification that the market value of the security added to such security pool equals or exceeds the market value of the security withdrawn from such security pool.
Cal. Code Regs. Tit. 2, § 16003.2.1