In reply to:

but my understanding of U.S. law is that anyone may change his/her name at any time without any formal legal process provided it is not done with the intent to defraud someone.

Like everything else, BYB, it varies from state to state. You have stated the basic common law rule. Some states have not changed from that rule, some states have substituted statutory procedures, and some (like Michigan) recognize both common law and statutory procedures. For what it's worth, in issuing passports the feds will recognize a name change legitimate in the resident state, including a common law change.