Okla. Stat. tit. 56, § 56-238.7: Modification of final order to pay child support

A final order of the Department of Human Services providing for

the payment of child support which has not been set aside on appeal

by the district court shall not be modified retroactively or payment

of all or a portion of the past due amount waived, except by mutual

agreement of the obligor and obligee or, if the child support rights

have been assigned to the Department or other entity, by agreement

of the Department or such entity.