Mass. Gen. Laws ch. 65 § 15A
Unless there is a specific provision to the contrary in the will or trust instrument under which a person is serving as executor, administrator or trustee, such person shall have the authority to settle or compromise, and to pay in advance of the statutory due date, any Massachusetts inheritance tax. Payment of such tax shall be made from the principal of the fund upon which the tax is computed, and, if more than one fund is involved, may be apportioned among such funds in an equitable manner. If any such person shall determine in good faith that payment of any such tax in advance of its statutory due date would be inequitable to any income beneficiary of such fund, such person may make appropriate adjustment or adjustments at any time or from time to time for the benefit of such income beneficiary from the principal of such fund; provided, however, that no such adjustment shall confer an inequitable benefit upon such income beneficiary.
Mass. Gen. Laws ch. 65, § 15A