(2) Certain retroactive plan amendments For purposes of this section, any amendment applying to a plan year which—
(A) is adopted after the close of such plan year but no later than 2½ months after the close of the plan year (or, in the case of a multiemployer plan, no later than 2 years after the close of such plan year),
(B) does not reduce the accrued benefit of any participant determined as of the beginning of the first plan year to which the amendment applies, and
(C) does not reduce the accrued benefit of any participant determined as of the time of adoption except to the extent required by the circumstances,
shall, at the election of the plan administrator, be deemed to have been made on the first day of such plan year. No amendment described in this paragraph which reduces the accrued benefits of any participant shall take effect unless the plan administrator files a notice with the Secretary of the Treasury notifying him of such amendment and such Secretary has approved such amendment, or within 90 days after the date on which such notice was filed, failed to disapprove such amendment. No amendment described in this subsection shall be approved by the Secretary of the Treasury unless such Secretary determines that such amendment is necessary because of a temporary substantial business hardship (as determined under
subsection (c)(2)) or a substantial business hardship (as so determined) in the case of a multiemployer plan and that a waiver under
subsection (c) (or, in the case of a multiemployer plan or a CSEC plan, any extension of the amortization period under
section 1084(d) of this title or section 1085a(d) of this title) is unavailable or inadequate.