grunion-field-html-filter.php

<?php

function modify_contact_form_field_html( $field_html, $field_label, $post_id ) {
        // Add HTML before the field.
        $field_html = '<span>Before the field.</span>' . $field_html;
        
        // Add HTML after the field.
        $field_html .= '<span>After the field.</span>';
 
        // Conditionally add based on field label and post id
        if( 123 == $post_id && 'First Name' == $field_label )
          $field_html .= '<span class="conditionally-added"></span>';
        
        return $field_html;
}

add_filter( 'grunion_contact_form_field_html', 'modify_contact_form_field_html', 10, 3 );

?>