Item 1, section 8 of the U. S. Constitution covers the powers of Congress. It states that only Congress can “coin money and regulate the value thereof “. No casino chip has ever been authorized by the U. S. Congress, therefore they are not coins.
Nevada Gaming Statutes specifally prohibit that a chip or token be made to "deceptively resemble" any coin of the United States or any other country. Nevada Gaming Statutes also describe what they are and the limitations on how they are to be used. To make any alteration to them while they are current would be “forgery“. There is a well defined process in the Gaming Statutes for retirement of these devices complete with a grace period for final redemption. Once the process is complete and these devices no longer have redeemable value they become simple merchandise or collectibles to some and therefore can be restored legally.

Both the U. S. Constitution and Nevada Gaming Statutes are availbe on the internet.