Foreign tax credit permits amendment of assessment when disputed foreign tax is settled and payment evidence is furnished. Where credit for income-tax paid in a foreign country or specified territory was not allowed because payment was under dispute, the Assessing Officer shall amend the assessment or intimation when the dispute is settled if the assessee, within six months from the end of the month in which the dispute is settled, submits evidence of settlement and payment and an undertaking that the credit has not been and will not be claimed for any other assessment year; the provisions of section 154 shall apply so far as may be.