The script must be included from a userscript with the following metablocks

• // @match https://www.youtube.com/*
• // @run-at document-start
• // @inject-into page
• // @grant none

Then an array window._ytConfigHacks will be provided and push your function into the array.

Testing

// ==UserScript==
// @name        New1235
// @namespace   Violentmonkey Scripts
// @match       https://greasyfork.org/*
// @grant       none
// @version     1.0
// @author      -
// @description 9/19/2023, 10:41:12 AM
// @require https://update.greasyfork.org/scripts/475632/1361351/ytConfigHacks.js
// ==/UserScript==
console.log(window._ytConfigHacks)
window._ytConfigHacks.add(function(){
console.log('test OK')
});
window.ytcsi={
tick:function(){}
}
window.yt={}
window.yt.config_={};
ytcsi.tick;

Real Example

// ==UserScript==
// @name        YouTube: Force Animated-Rolling-Number for Live
// @namespace   Violentmonkey Scripts
// @match       https://www.youtube.com/*
// @grant       none
// @version     1.0
// @author      -
// @description 9/19/2023, 9:32:49 AM
// @run-at      document-start
// @inject-into page
// @unwrap
// @require https://update.greasyfork.org/scripts/475632/1361351/ytConfigHacks.js
// ==/UserScript==
(() => {
let mex = 0;
window._ytConfigHacks.add((config_) => {
let EXPERIMENT_FLAGS = null;
EXPERIMENT_FLAGS = config_.EXPERIMENT_FLAGS || 0;
if (EXPERIMENT_FLAGS) {
if (!mex) {
mex = 1;
console.log('EXPERIMENT_FLAGS detected')
}
EXPERIMENT_FLAGS.web_enable_dynamic_metadata = true;
EXPERIMENT_FLAGS.dynamic_metadata_update_interaction_delay_period_sec = 8;
}
});
})();

Scripts Using this Library

• https://greasyfork.org/en/scripts/470428-youtube-experiment-flags-tamer
• https://greasyfork.org/en/scripts/471033-youtube-force-html5-exponential-memory-for-sticky
• https://greasyfork.org/en/scripts/472945-polymer-enable-controller-extraction
• https://greasyfork.org/en/scripts/475635-youtube-force-animated-rolling-number