Any letter of credit issued, confirmed or advised under an USAID letter of commitment and any agreement relating to such letter of credit or to instructions for payment issued by an approved applicant shall not be inconsistent with or contrary to the terms of the letter of commitment. Any such letter of credit or agreement may be modified or extended at any time in such a manner and to such extent as is acceptable to the approved applicant and the bank: Provided, That such modification or extension may not be inconsistent with or contrary to the terms of the letter of commitment. In the case of any inconsistency or conflict between the terms and conditions of the letter of commitment and the instructions of the approved applicant, the terms and conditions of the letter of commitment shall control.