Just install the module and customize it via hooks in /site/init.php (not ready.php):
// dont show message after set maxDays
$wire->addHookAfter("RockBirthday::setConfig", function($event) {
$event->object->maxDays = 30; // 14 is default
});
// get date of birth of user
// must return a timestamp (int)
$wire->addHookAfter("RockBirthday::getBirthdate", function($event) {
$user = $this->user;
$event->return = $user->getUnformatted('your_birthdate_field');
});
// get markup of message
$wire->addHookAfter("RockBirthday::getMarkup", function($event) {
$user = $this->user;
$html = "<h1>Happy Birthday, {$user->name}!</h1>";
$event->return = "<script>vex.open({unsafeContent: \"$html\"});</script>";
});