Hello.
Then we can go this way and try some customization of default web part, however, maybe we can solve it in another way, as we already have built-in functionality allowing users comment any article on your site. Beside some special implementations, like Comment view web part for Blog posts, we have Message boards module. The Message boards module enables site visitors to comment on the content of a particular page. You can find more info including some example
here. Would this solution be OK with you, or can't you use it for some reason, like insufficient license edition? Thank you.
Best Regards,
Radek Macalik