(a) For purposes of computing its net income under this chapter, a taxpayer shall add back otherwise deductible interest paid, accrued or incurred to a related member, as defined in section 31I, during the taxable year, except that a deduction shall be permitted when either:

1. (1) the taxpayer establishes by clear and convincing evidence, as determined by the commissioner, that the disallowance of the deduction is unreasonable, or (2) the taxpayer and the commissioner agree in writing to the application of an alternative method of apportionment under section 42. Nothing in this subsection shall be construed to limit or negate the commissioner's authority to otherwise enter into agreements and compromises otherwise allowed by law.