Upon expiration of the term of the HAP contract, HUD and the Borrower may agree (subject to available funds) to extend the term of the HAP contract or to renew the HAP contract. The number of assisted units under the extended or renewed HAP contract shall equal the number of assisted units under the original HAP contract, except that:

(a) HUD and the Borrower may agree to reduce the number of assisted units by the number of assisted units that are not occupied by eligible families at the time of the extension or renewal; and

(b) HUD and the Borrower may agree to permit reductions in the number of assisted units during the term of the extended or renewed HAP contract as assisted units are vacated by eligible families. Nothing in this section shall prohibit HUD from reducing the number of units covered under the extended or renewed HAP contract in accordance with §891.575(b).