pocketmine\event\player\PlayerPreLoginEvent::setKickMessage PHP Method

    public function setKickMessage($kickMessage)
    {
        $this->kickMessage = $kickMessage;
    }

 /**
  * @param PlayerPreLoginEvent $login
  * @priority HIGH
  * @ignoreCancelled true
  */
 public function onPlayerPreconnect(PlayerPreLoginEvent $login)
 {
     $name = strtolower($login->getPlayer()->getName());
     if (in_array($name, ["pocketmine", "console", "server", "rcon", "legionpe", "botbot", "fakeclient", "pocketbot"])) {
         $login->setCancelled();
         $login->setKickMessage("Bad username");
     } else {
         $reason = $this->getMain()->getMySQLi()->query("SELECT msg FROM ipbans WHERE %s LIKE ip AND %d<(unix_timestamp(creation)+length);", MysqlConnection::ASSOC, $login->getPlayer()->getAddress(), time());
         if (is_array($reason)) {
             $login->setCancelled();
             $login->setKickMessage("You are IP-banned! Reason: " . (isset($reason["msg"]) ? $reason["msg"] : "no reason specified :("));
         }
         if (($old = $this->getMain()->getServer()->getPlayerExact($name)) instanceof Player) {
             // if has name collision
             if ($old->getAddress() !== ($ip = $login->getPlayer()->getAddress())) {
                 // if IP is different
                 if (substr($ip, 0, 8) !== "192.168." and $ip !== "119.247.51.252") {
                     // if new IP isn't local and isn't PEMapModder's IP address (yes I am making it for myself)
                     $login->setCancelled();
                     $login->setKickMessage("Player already online with differnet IP");
                 }
             }
         }
     }
 }