The only thing the flag code says about the design of the flag itself is below. Everything else is about how the flag should be treated, used, and displayed:
"§1. Flag; stripes and stars on
The flag of the United States shall be thirteen horizontal stripes, alternate red and white; and the union of the flag shall be fifty stars representing the fifty states, white in a blue field
§2. Same; additional stars
On the admission of a new State into the Union one star shall be added to the union of the flag; and such addition shall take effect on the fourth day of July then next succeeding such admission"
I know that France recently altered the shade of blue that they use to be a darker one on their flag, so there is probably some variability in a number of countries.
The flag code isn't about legality. It is considered improper to fly the flag different ways but they aren't illegal. So yes, the 1st amendment of the constitution would mean you could fly the flag however you wished without being arrested. That doesn't mean someone won't punch you over it though
According to the U.S. Army Institute of Heraldry, the United States flag never becomes obsolete. Any approved American flag may continue to be used and displayed until no longer serviceable.[188]
The "Grand Union Flag", or the "Continental Colours", (also known as the "Congress Flag", the "Cambridge Flag", and the "First Navy Ensign") was the first national flag of the United States of America. First hoisted on December 3, 1775 by naval officer John Paul Jones, the flag was used heavily by the Second Continental Congress of the United States, as well as by Commander George Washington in his Continental Army during the early years of the American Revolutionary War.
Similar to the current U.S. flag, the Grand Union Flag has 13 alternating red and white stripes, representative of the Thirteen Colonies. The upper inner corner, or canton, features the Union Jack, or flag of the Kingdom of Great Britain, of which the colonies were subjects.