Destroying money is illegal.
I often get asked if making a coin ring is against the law. While coins altered for the purpose of counterfeiting are illegal, as long as an altered coin is not being done so with the intent to counterfeit, then it is not illegal… at least in the United States....
“Section 331 of Title 18 of the United States code provides criminal penalties for anyone who “fraudulently alters, defaces, mutilates impairs, diminishes, falsifies, scales, or lightens any of the coins coined at the Mints of the United States.” This statute means that you may be violating the law if you change the appearance of the coin and fraudulently represent it to be other than the altered coin that it is. As a matter of policy, the U.S. Mint does not promote coloring, plating or altering U.S. coinage: however, there are no sanctions against such activity absent fraudulent intent.”
The key words in the statute above is “fraudulent intent”. If you altered a piece of US currency, and then knowingly attempted to use it to make a purchase or to represent it as something other than an altered coin, that would be fraudulent intent, and that is illegal. (An example of this illegal fraudulent intent would be altering a US $1.00 bill and attempting to pass it off as a $20.00 bill.)
https://coinringusablog.com/frequently-asked-questions/
#6 The Bank of Canada is warning people to stop drawing Spock on their money
http://newsinstact.com/earth/the-bank-of-canada-is-warning-people-to-stop-drawing-spock-on-their-money/
They are “improving” the money. : )