.replaceWith()
replaces an entire DOM element. What you are trying to do is to change the some of the text of a single text node which is part of an element. There is no single function in the DOM or in jQuery that changes just part of a text node or part of the text of an element. The only way you do that is to fetch the text, make the changes you want to it and set it back.
You could create your own jQuery method that would do that.
$.fn.replaceText = function(srcText, replacementText) {
return this.each(function() {
var item = $(this);
var txt = item.text();
item.text(txt.replace(srcText, replacementText));
});
}
Working demo: http://jsfiddle.net/jfriend00/U8k8C/