If a trustee determines that an allocation between principal and income required by sections 557A-409 through 557A-412 or section [557A-415] is insubstantial, the trustee may allocate the entire amount to principal if one of the circumstances described in section 557A-104(c) does not apply to such an allocation. This power may be exercised by a co-trustee in the circumstances described in section 557A-104(d), and it may be released for the reasons and in the manner described in section 557A-104(e). An allocation shall be presumed to be insubstantial if:
(1) The amount of the allocation would increase or decrease an accounting period's net income, as determined before the allocation, by less than ten per cent; or
(2) The value of the asset producing the receipt for which the allocation would be made is less than ten per cent of the total value of the trust's assets at the beginning of the accounting period.