<!DOCTYPE html>
<html>
<head>
</head>
<body>
<div id="dont-replace-them">
New York<br />
</div>
<br />
<div id="replace-them">
New York<br />
</div>
<script type="text/javascript">
function replaceWords() {
document.getElementById("replace-them").innerHTML = document.getElementById("replace-them").innerHTML.replace("New York", "New York City");
}
replaceWords();
</script>
</body>
</html>