How To Customise WordPress Comment Submit Button?

You can modify a lot of form behavior by passing $args to the comment_form() function – have you tried that?

Alternatively, you can write a custom comments template file and then use the comments_template() call to display it within the theme. This method would allow you to have complete control of the type, class, and ID of any field, provided that you hooked in to the proper WordPress functions to handle comment submission.