Correct - to affect a video that has been added by a user clicking the uploaded file to add it to the editor, you would need to modify a JS file (and even then, it's not a file but a row in the database...and you don't have access to that, and it would be updated on every upgrade anyway)
There are other ways to apply it but it requires a plugin/application to do it. I've got it as a feature in https://www.ynwa.tv/files/file/38-ne-html5-audiovideo-player/ but that would be hitting a small nail with a very large hammer if your requirement is simply to add that controlslist.