Youtube_Gaming_Feedly.user.js

// ==UserScript==
// @name        Youtube Gaming Feedly
// @namespace   numuon.me
// @description Change Youtube links in Feedly to Youtube Gaming links.
// @include     https://feedly.com/*
// @version     1.1
// @grant       none
// @require     http://code.jquery.com/jquery-1.9.1.min.js
// ==/UserScript==

$(document).ready(function() {
    window.setInterval(function() {
        $('a').each(function(i, thisLink) {
            thisLink.href = thisLink.href.replace('www.youtube.com/watch?','gaming.youtube.com/watch?');
        });
    }, 500);
});

Youtube_Gaming_Linker.user.js

// ==UserScript==
// @name        Youtube Gaming Linker
// @namespace   numuon.me
// @description Change all Youtube links to Youtube Gaming links.
// @exclude     https://www.youtube.com/*
// @version     1.1
// @grant       none
// ==/UserScript==

var links,thisLink;
links = document.evaluate("//a[@href]",
    document,
    null,
    XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
    null);
for (var i=0;i<links.snapshotLength;i++) {
    var thisLink = links.snapshotItem(i);
    thisLink.href = thisLink.href.replace('www.youtube.com/watch?','gaming.youtube.com/watch?');
}

Youtube_Gaming_Redirect.user.js

// ==UserScript==
// @name        Youtube Gaming Redirect
// @namespace   numuon.me
// @description Redirects Youtube to Youtube Gaming.
// @include     https://www.youtube.com/watch?*
// @version     1.1
// @grant       none
// ==/UserScript==

window.location.replace(window.location.href.replace("www.youtube.com/watch?","gaming.youtube.com/watch?"));