Вы можете подключиться к before_send_mail
и обновить сообщение на основе указанного поля c.
add_action ('wpcf7_before_send_mail', 'dd_before_send_mail');
function dd_before_send_mail($contact_form){
// Get the instance
$submission = WPCF7_Submission :: get_instance();
if ($submission){
$fields = $submission->get_posted_data();
// put your field name in for [your-field]
if (intval($fields['your-field'] ) > 10 ) {
$contact_form -> set_properties(array('messages' => array('mail_sent_ok' => 'This is your message')));
}
}
}