You will need some way of extending the 50hr Developer Mode limit. Then remove YouTube before installing this version and then disable application updates so that the official version does not get installed. Now follow the LG SDK guides on how to install IPK files and enable Developer Mode and install the keys to your computer. This unofficial homebrew channel will have the youtube adblock ipk installable. If you don't like to compile (though you will need to run the webos sdk anyways to install ipk's)

Sign up for a WebOS Developer account and compile this ipk - it has advert blocking and sponserblock, also find the add-on to automatically extend the developer mode timeout. In addition to this, YouTube will now give some creators the opportunity to offer free or paid courses ‘to provide in-depth, structured learning experiences for viewers’.I've done this on my Nanocell 4K tv running WebOS 5.3 - I'd highly recommend disabling application and WebOS updates to prevent any changes LG could make. YouTube says that the new Player for Education improves on the Classroom experience, offering enhancements to these users also. Worth noting, too, that YouTube is already available via Google Classroom, which is now used by over 150 million students, educators and school leaders around the world. YouTube says that it’s partnering with established edtech companies like EDpuzzle, Purdue University and Purdue Global on the initial stages of the initiative, with further expansion planned in the near future.

That will make it easier for teachers to use YouTube content within their curriculum, and to share relevant links with students without additional disruptions.

“To improve the YouTube experience in educational environments, we're launching YouTube Player for Education - a new YouTube embedded player that shows content on commonly used education apps without distractions like ads, external links or recommendations.”

How much is ad free youtube