Originally, and still today, "ringing the changes" means bell ringers going through their tuneful tintinnabulations, a "change" being the list of bell pulls issued to the ringers to make the eventual tune. This expression found its way to the world of horse racing where a "ringer" was a better horse than the one entered in a race secretly substituted so as to fool others for financial gain. It is possible that the metaphor here was that the two horses were as alike as two bells that sounded the same note. It later came to mean any fraudulent substitution e.g. a motor car offered for sale that has been given a new identity, possibly having been reconstructed from one or more wrecks, but offered as an unblemished vehicle.
This idea has been extended in the UK to mean anything that looks like something else, but not necessarily with any element of fraud. For example, show business impersonators are said to be "dead ringers" for those that they imitate. The addition of the word "dead" gives additional emphasis, and is a common North Western dialect adjective giving emphasis.