Code:
// ==UserScript==
// @name NewPost to LastPost
// @version 0.1
// @description Changes the url from "newpost" to "lastpost".
// @author https://nulledbb.com/profile/6429
// @match https://nulledbb.com/*
// ==/UserScript==
windows.location = window.location.replace('action=newpost', 'action=lastpost');