A multiemployer plan, other than a plan which primarily covers employees in the building and construction industry, may be amended to provide that the amount of unfunded vested benefits allocable to an employer that withdraws from the plan is an amount determined under paragraph (2), (3), (4), or (5) of this subsection, rather than under subsection (b) or (d). A plan described in
section 1383(b)(1)(B)(i) of this title (relating to the building and construction industry) may be amended, to the extent provided in regulations prescribed by the corporation, to provide that the amount of the unfunded vested benefits allocable to an employer not described in
section 1383(b)(1)(A) of this title shall be determined in a manner different from that provided in subsection (b).