PacketPlayOutPlayerListHeaderFooter packet = new PacketPlayOutPlayerListHeaderFooter();
IChatBaseComponent header = ChatSerializer.a("Your Json Header");
IChatBaseComponent footer = ChatSerializer.a("Your Json Footer");
try {
    Field a = packet.getClass().getDeclaredField("a");
    a.setAccessible(true);
    a.set(packet, header);
    Field b = packet.getClass().getDeclaredField("b");
    b.setAccessible(true);
    b.set(packet, footer);
} catch (Exception e) {
    e.printStackTrace();
}
((CraftPlayer) player).getHandle().playerConnection.sendPacket(packet);