function wpcf7_do_something_else($cf7) {
$wpcf = WPCF7_ContactForm::get_current();
if(isset($_POST['your-message']) && !empty($_POST['your-message'])) {
$props = $wpcf->get_properties();
if(isset($props['mail_2'])) {
$props['mail_2']['body'] = 'Лалалала я заменил текст';
$wpcf->set_properties($props);
}
}
return $wpcf;
}