The amount of any penalty or assessment which has become final, or for which a judgment has been entered under §35.42 or §35.43, or any amount agreed upon in a compromise or settlement under §35.46, may be collected by administrative offset under 31 U.S.C. 3716, except that an administrative offset may not be made under this subsection against a refund of an overpayment of federal taxes, then or later owing by the United States to the defendant.