united-states president
Can the President unilaterally change the design of the US flag?
<p>In researching this question, I found <a href="https://www.gpo.gov/fdsys/pkg/USCODE-2011-title4/html/USCODE-2011-title4-chap1.htm" rel="noreferrer">this page from the Government Publishing Office</a>, which states in 4 U.S.C. §10:</p>

<blockquote>
  <p>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pertaining to the display of the flag of the United States of America, set forth herein, may be altered, modified, or repealed, or additional rules with respect thereto may be prescribed, by the Commander in Chief of the Armed Forces of the United States, whenever he deems it to be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.</p>
</blockquote>

<p>§1 describes the design of the flag, which I interpret as a rule or custom pertaining to the display of the flag.</p>

<p>I'm not a lawyer though.  Can POTUS change the design of the US flag without an act of Congress?</p>

<p>§1 states what the design of the flag shall be (§2 mandates addition of stars when a new state is added). In essence, 4 USC 1-2 define what the flag is, and the rest of that chapter addresses what you can do with it. These are laws (passed by Congress), not rules or customs. That is, it's not a custom that the flag is 50 starts and 13 stripes, it's the law. POTUS cannot unilaterally change the law. (4 USC 3 also specifies punishments for certain kinds of flag abuse, and this too is outside the scope of that the president can do by declaration). 4 USC 5 in fact states that "The flag of the United States for the purpose of this chapter shall be defined according to sections 1 and 2 of this title", and that</p>

<blockquote>
  <p>The following codification of existing rules and customs pertaining to
  the display and use of the flag of the United States of America is
  established for the use of such civilians or civilian groups or
  organizations as may not be required to conform with regulations
  promulgated by one or more executive departments of the Government of
  the United States.</p>
</blockquote>

<p>§§6-9 specify standard flag etiquette (violation of which incurs no legal punishment), and those are the rules that the president can rewrite.</p>
