The tax administrator, with the approval of the attorney general, may effect a settlement of the amount of any taxes imposed by chapter 22 of this title as they deem to be for the best interests of the state, and the payment of amount agreed upon is a full satisfaction of the taxes; provided, that the settlement and assessment are made only with the consent of the executor of the will or the trustee under the other instrument, or, in the case of a transfer by will of real estate, of the persons entitled to the real estate, or, if the real estate passes to a trustee for those persons, then of the trustee. The settlement, in accordance with the provisions of this section, of a tax upon any transfer of property subject to a power of appointment, if the agreement of settlement provides, precludes the assessment under this chapter or under any act hereafter passed of any further tax, with respect to the right to transfer, upon or with respect to the transfer of any property at the time subject to the power, as a part of the estate of the donee of the power. The agreement is binding upon all persons taking property subject to the tax, except for fraud or manifest error; and executors and trustees are expressly authorized to enter into an agreement unless a contrary intention appears in the instrument defining their powers.