(a) General rule. A plan using any of the allocation methods described in §§ 4211.32 through 4211.34 may, by plan amendment and without PBGC approval, adopt any of the modifications described in this section. In determining the numerators and the denominators in paragraph (d) of this section, the rules under § 4211.4 (and permissible simplified methods under §§ 4211.14 and 4211.15) apply.

(b) Restarting initial liabilities. A plan may be amended to allocate the initial plan year unfunded vested benefits under § 4211.32(b), § 4211.33(b), or § 4211.34(b) without separately allocating to employers the liabilities attributable to their participation under their prior plans. An amendment under this paragraph must include an allocation fraction under paragraph (d) of this section for determining the employer's proportional share of the total unfunded benefits as of the close of the initial plan year.

(c) Amortizing initial liabilities. A plan may by amendment modify the amortization of initial liabilities in either of the following ways:

(1) If two or more plans that use the presumptive allocation method of section 4211(b) of ERISA merge, the merged plan may adjust the amortization of initial liabilities under § 4211.32(b) to amortize those unfunded vested benefits over the remaining length of the prior plans' amortization schedules.

(2) A plan that has adopted the allocation method under § 4211.33 or § 4211.34 may adjust the amortization of initial liabilities under § 4211.33(b) or § 4211.34(b) to amortize those unfunded vested benefits in level annual installments over any period of at least five and not more than fifteen years.

(d) Changing the allocation fraction. A plan may by amendment replace the allocation fraction under § 4211.32(b), § 4211.33(b), or § 4211.34(b) with any of the following contribution-based fractions—

(1) A fraction, the numerator of which is the total amount required to be contributed under the merged and prior plans by the withdrawing employer in the 60-month period ending on the last day of the initial plan year, and the denominator of which is the sum for that period of the contributions made by all employers that had not withdrawn as of the end of the initial plan year;

(2) A fraction, the numerator of which is the total amount required to be contributed by the withdrawing employer for the initial plan year and the four preceding full plan years of its prior plan, and the denominator of which is the sum of all contributions made over that period by employers that had not withdrawn as of the end of the initial plan year; or

(3) A fraction, the numerator of which is the total amount required to be contributed to the plan by the withdrawing employer since the effective date of the merger, and the denominator of which is the sum of all contributions made over that period by employers that had not withdrawn as of the end of the initial plan year.