(a)(1) If by reason of the death of a decedent property passes or is acquired under a beneficiary designation, a will or trust of a decedent who dies after December thirty-first, two thousand nine and before January first, two thousand eleven, that contains a bequest or other disposition based upon the amount of property that can be sheltered from federal estate tax by referring to the "unified credit", "estate tax exemption", "applicable exclusion amount", "applicable exemption amount", "applicable credit amount", "marital deduction", "maximum marital deduction", "unlimited marital deduction", "charitable deduction", "maximum charitable deduction" or similar words or phrases relating to the federal estate tax, or that measures a share of an estate or trust based on the amount that can pass free of federal estate taxes, or that is otherwise based on a similar provision of federal estate tax then such beneficiary designation, will or trust shall be deemed to refer to the federal estate tax law as applied with respect to decedents dying in two thousand ten, regardless of whether an election is made not to have the federal estate tax apply to a particular estate.
(2) If by reason of the death of a decedent property passes or is acquired under a beneficiary designation, a will or trust of a decedent who dies after December thirty-first, two thousand nine and before January first, two thousand eleven, that contains a bequest or other disposition based upon the amount of property that can be sheltered from federal generation-skipping transfer tax by referring to the "generation-skipping transfer tax exemption", "GST exemption", "generation-skipping transfer tax", "GST tax" or similar words or phrases that measures a share of an estate or trust based on the amount that can pass free of federal generation-skipping transfer taxes, or that is otherwise based on a similar provision of federal generation-skipping transfer tax law, then such beneficiary designation, will or trust shall be deemed to refer to the federal generation-skipping transfer tax law in effect in two thousand ten, regardless of whether an election is made not to have the federal estate tax apply to a particular estate.
(3) This paragraph shall not apply to a beneficiary designation, will or trust that manifests an intent that a contrary rule shall apply.
(b) The executor, trustee or other interested person under a beneficiary designation, will or trust referred to in paragraph (a) of this section may bring a proceeding to determine whether the beneficiary designation, will or trust manifests a contrary intention within the meaning of subparagraph three of paragraph (a) of this section. In any such proceeding, extrinsic evidence may be admitted to establish the decedent's intent.
(c) Any proceeding described in paragraph (b) of this section must be commenced by the date which is (1) twenty-four months following the date of death of the decedent, testator or grantor or (2) six months following the day on which the chapter of the laws of two thousand eleven which amended this paragraph became a law, whichever date is later, and not at any time thereafter. Notwithstanding the foregoing, the time to commence such a proceeding may be extended, in the discretion of the court, on a petition showing reasonable cause and on notice to such persons and in such manner as the court may direct.