Alarm message has major priority of Alert message.

Ah, okay....now I understood your problem

I would try the following:

• Write your own plugin that establishes an new connection to an equal plugin on the other side. You can use everything of JavaAPI in plugins, maybe you will need additional libraries, but it should be possible.
• Your plugin needs to implement the PacketInterceptor interface. Also you need an (empty) implementation of the Component interface.
• Use the interceptor to scan processed packets for outgoing high priority messages. Send a copy of these packets through your high priority connection. You will need to drop the high priority packets, so they are not send through the normal connection. Therefor you will need to distinguish between IQ and other packets:
• IQ packets cannot be dropped without returning an error, so you will need to reroute them to your own component, so they run into trash. Just set Packet#setTo(componentJID);
  

• For other packets throw an PacketRejectedException

• When your plugin recieves packets over the high priority connection, you can simply inject them into Openfire by using PacketRouter#route(packet); Make sure your plugin does not intercept such packets again and sends them back...
• You could also switch the roles of high an low priority, simply what makes more sense for you.