Most strings and form fields may be controlled through the $args array passed into the function, while you may also choose to use the {@see 'comment_form_default_fields'} filter to modify the array of default fields if you'd just like to add a new one or remove a single field. All fields are also individually passed through a filter of the {@see 'comment_form_field_$name'} where $name is the key used in the array of fields.