Within the sixty-day period and before the adoption of any resolution disapproving a plan, the Secretary may withdraw or amend such plan: Provided, That any amendments affecting the division of an award between two or more beneficiary entities shall be subject to the consent of these entities as provided in section
1402
(d) of this title. Any such amended plan shall become valid at the end of a sixty-day period beginning on the day such amendment is submitted to the Congress, unless during such sixty-day period, a joint resolution is enacted disapproving such plan as amended.