A little note for fun

Complement to the order of February 16th, 1859, establishing a “normal tuning fork” in the country of France.
Art. 1st - Music composers will be willing to put themselves in accordance with the forgoing order.
Art. 2 - As an example, Mr Wolfgang Amadeus Mozart will be asked to rewrite the Overture of its opera Don Giovanni in C-sharp minor, instead of D minor, to ensure compliance with the “normal tuning fork” in 435 vibrations per second used in our country, giving up that of 415 vibrations per second that he has considered to be permitted to use. Failing which, the performance of his opera will be forbidden on all public stages in France. It ensues from it that the various airs of this opera written in other tones must be rewritten into the same scale.