(a) If the amount of federal estate tax is, upon the final determination of the federal estate tax, increased or decreased as affecting an estate the transfer of any part whereof is taxable hereunder subsequent to the payment of the Tennessee estate tax, the Tennessee estate tax imposed shall be changed accordingly. Any additional estate tax shall be payable at the same time or times at which the additional federal estate tax is payable.

(b) In the event that there shall be a decrease in the federal estate tax, the executor shall file with the commissioner of revenue an affidavit in such form as is prescribed by the commissioner, setting forth the amount of:

(1) Federal estate tax as originally computed;

(2) Federal estate tax as revised and decreased;

(3) Tennessee estate tax theretofore paid and date of payment; and

(4) Tennessee estate tax properly payable in view of such revision and decrease of federal estate tax.

(c) With the affidavit, there shall also be filed:

(1) A certificate or other evidence from the internal revenue service showing the amount of federal estate tax as so revised and decreased;

(2) A certified copy of the affidavit filed with the commissioner as provided in § 67-8-206;

(3) A duplicate receipt by the commissioner for the Tennessee estate tax theretofore paid, showing date of payment; and

(4) Such other evidence as the commissioner may require in order to enable the commissioner to determine the Tennessee estate tax, properly payable, and the amount, if any, of any refund due.

(d) The commissioner shall thereupon cause to be paid to the executor the amount of refund found to be due, together with interest thereon as provided in § 67-1-801(b).