jlong

var parser = document.createElement('a');
parser.href = "http://example.com:3000/pathname/?search=test#hash";

parser.protocol; // => "http:"
parser.hostname; // => "example.com"
parser.port;     // => "3000"
parser.pathname; // => "/pathname/"
parser.search;   // => "?search=test"
parser.hash;     // => "#hash"
parser.host;     // => "example.com:3000"

evert

// ==UserScript==
// @name           Referral: your mom
// @namespace      yourmom
// @description    This script changes every utm_source variable in links to 'Your mom'.
// @include        *
// ==/UserScript==

var links = document.getElementsByTagName('a');
for(var i=0; i<links.length; i++) {
   links[i].href = links[i].href.replace(/([&|?])utm_source=(.*)([&|?|^])/,"$1utm_source=Your+mom$3");