Modifying sent packets/Sending packets

Ok so I need to have a server only nbt tag. My current idea is to modify the packets send by pocketmine to the client and remove the nbt tag. How do I do this ?

Here is my current code (I'm cancelling the packet to send a new one):

PHP:

    public function onPacketSend(DataPacketSendEvent $event) {
        $packet = $event->getPacket();
        $player = $packet->getPlayer();
        $class = get_class($packet);
        echo $class . "\n";
        if ($class == "pocketmine\\network\\mcpe\\protocol\\InventorySlotPacket") {
            $event->setCancelled(true);
            $newPacket = new InventorySlotPacket();
        } else if ($class = "pocketmine\\network\\mcpe\\protocol\\InventoryContentPacket") {
            //$event->setCancelled(true);
        } else if ($class = "pocketmine\\network\\mcpe\\protocol\\") {
            $event->setCancelled(true);
        }
    }


 

Why you want to do that?