Comment form above comments with a plugin?

Hi,

I'd like to move the comment form for new comments above the existing comments.

I've already found this page that provides the PHP code to do so.

However, I'd rather not use a child theme.

I found this page about adding PHP.

I'm already using the 'Code Snippets' plugin for adding a a couple of functions to my site. But I don't think you can use Code Snippets to override the existing comments.php file?

The other option on the page is creating a custom plugin. This should be able to override the existing comments.php file, right?
If so, is there anything I need to add to the code provided here to do so?

Thanks in advance!