Any rule or custom pertaining to the display of the flag of the United States of America, set forth herein, may be altered, modified, or repealed, or additional rules with respect thereto may be prescribed, by the Commander in Chief of the Armed Forces of the United States, whenever he deems it to be appropriate or desirable; and any such alteration or additional rule shall be set forth in a proclamation.
4 U.S. Code § 10 - Modification of rules and customs by President
The flag of the United States of America is universally representative of the principles of the justice, liberty, and democracy enjoyed by the people of the United States; and
People all over the world recognize the flag of the United States as symbolic of the United States; and
The effective prosecution of the war requires a proper understanding by the people of other countries of the material assistance being given by the Government of the United States:
NOW, THEREFORE, by virtue of the power vested in me by the Constitution and laws of the United States, particularly by the Joint Resolution approved June 22, 1942, as amended by the Joint Resolution approved December 22, 1942 [now sections 4 to 10 of this title], as President and Commander in Chief, it is hereby proclaimed as follows:
1. The use of the flag of the United States or any representation thereof, if approved by the Foreign Economic Administration, on labels, packages, cartons, cases, or other containers for articles or products of the United States intended for export as lend-lease aid, as relief and rehabilitation aid, or as emergency supplies for the Territories and possessions of the United States, or similar purposes, shall be considered a proper use of the flag of the United States and consistent with the honor and respect due to the flag.
2. If any article or product so labelled, packaged or otherwise bearing the flag of the United States or any representation thereof, as provided for in section 1, should, by force of circumstances, be diverted to the ordinary channels of domestic trade, no person shall be considered as violating the rules and customs pertaining to the display of the flag of the United States, as set forth in the Joint Resolution approved June 22, 1942, as amended by the Joint Resolution approved December 22, 1942 (U.S.C., Supp. II, title 36, secs. 171–178) [now sections 4 to 10 of this title] for possessing, transporting, displaying, selling or otherwise transferring any such article or product solely because the label, package, carton, case, or other container bears the flag of the United States or any representation thereof.