gistfile1.js

// ==UserScript==
// @name           replace_ritsboy
// @namespace      jp.hakobe.gm
// @include        http://twitter.com/.*
// ==/UserScript==


var nodes = document.getElementsByClassName('status-body');
for (var i in nodes) {
	var node = nodes[i].childNodes[1].childNodes[1].firstChild;
	if (node.innerHTML == 'ritsboy') {
		node.innerHTML = 'udonchan';
		node.setAttribute('title', 'udonchan');
	}
}