Sorry, I haven't found the answer to this, though there is already a forum topic about it:
Can I use a certain tag when writing a article in order to not allow comments on this certain article? I know I can exclude a certain id in the settings.
Further on, if there is a tag like this, would it be possible to have a button for this in the text editor when creating articles?
No, right now there isn't. The problem is that such a tag can only work with com_content and not to 100%. The problem is that if you add such a tag to your text it will be saved in the fulltext field in the database. But when you are on the frontpage, the com_content component doesn't load the fulltext and I can't parse it to look for this tag.
That is why the only option is add the id of the article in the settings. Right now I haven't figured a better way to do this.