I wouldn't advertise you are using coins for oher than spending. It is a major no no.
No it's not, it is one hundred percent ok to do that.
Is it legal?
Yes, The United States Codes under Title 18, Chapter 17, and Section 331, prohibits the mutilation, diminution and falsification of United States coinage.
However, it has been the opinion of some individual officers at the Treasury Department, though without any indication of approval, the foregoing statute does not prohibit the mutilation of coins if done without fraudulent intent or if the mutilated coins are not used fraudulently.
So you just can't sell it after you make it