user.js

// ==UserScript==
// @name         Slack偽装
// @namespace    io.plusminus.userscript.slack.fuck
// @version      0.1
// @match        https://*.slack.com/*
// @grant        none
// @require      https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js
// ==/UserScript==

const config = {
    userId: '',
    userName: '',
    dummyName: '†真名†',
    dummyIcon: 'https://github.com/mohemohe.png',
};

const body = document.querySelector('body');
const mo = new MutationObserver(_.debounce(changes => {
    const names = document.querySelectorAll(`.c-message__sender > a[href="/team/${config.userId}"]`);
    if (names) {
        Array.from(names).forEach(name => {
            name.innerHTML = config.dummyName;
        });
    }
    const links = document.querySelectorAll(`.c-member_slug--mention[href="/team/${config.userId}"]`);
    if (links) {
        Array.from(links).forEach(link => {
            link.innerHTML = `@${config.dummyName}`;
        });
    }
    const icons = document.querySelectorAll(`.c-avatar[href="/team/${config.userId}"] > img`);
    if (icons) {
        Array.from(icons).forEach(icon => {
            icon.src = config.dummyIcon;
        });
    }
    const messages = document.querySelectorAll('.c-message__body');
    if (messages) {
        Array.from(messages).forEach(message => {
            message.innerHTML = message.innerHTML.replace(new RegExp(config.userName, 'g'), config.dummyName);
        });
    }
}), 1000);
mo.observe(body, {
    childList: true,
    subtree: true,
});