Adds a reply to message button in all of your own messages's popups in Stack Exchange chatrooms.

SO-self-reply.js

// ==UserScript==
// @name         Self-Reply Button
// @version      0.1
// @description  Adds a reply to message button in all of your own messages's popups in Stack Exchange chatrooms.
// @author       12944qwerty
// @include      http://chat.stackoverflow.com/rooms/*
// @include      https://chat.stackoverflow.com/rooms/*
// @require      http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js
// @require      https://gist.github.com/raw/2625891/waitForKeyElements.js
// ==/UserScript==

waitForKeyElements(
    '.popup',
    function(popup) {
        popup = popup.get(0);
        if (!popup.innerHTML.includes("reply to this message")) { // If it is included, it is not my own message
            var messageID = popup.children[1].children[1].href;
            messageID = messageID.substring(messageID.indexOf("#")+1);
            popup.innerHTML = '<div class="btn-close">X</div><div><span title="Wed 22:06">posted 2d ago</span> – <a rel="noreferrer noopener" href="/transcript/message/52335457#52335457">permalink</a><br></div><span class="reply" onclick="(function() {var inBox = document.getElementById(&quot;input&quot;);inBox.value=&quot;:' + messageID + '&quot; + &quot; &quot; + inBox.value;})();"><span class="newreply"> </span> reply to this message</span><br><br><span class="flag" title="Moderator flags are seen only by the site-moderators, and should be used to indicate serious issues with a message, and other administrative issues.">flag for moderator</span>';
        }
    }
);