Any allocation of volume cap for the issuance of private activity bonds constituting qualified mortgage bonds, within the meaning of Section 143 of the Code, shall, when made to an authorized issuer of qualified mortgage credit certificates within the meaning of Section 25 of the Code, include the authority of such issuer to elect not to issue such qualified mortgage bonds so as to entitle such issuer to issue such certificates pursuant to Section 25 of the Code. In addition, the ability to assign, reallocate or carry-forward any allocation of volume cap for the issuance of private activity bonds constituting qualified mortgage bonds shall include the authority to elect not to issue such qualified mortgage bonds from such assigned, reallocated or carry-forward allocation of volume cap so as to allow the issuance of qualified mortgage credit certificates.