If a receiver specifies an ACL type (which is probably should) when an incorrect ACL is published to that queue the Agent will raise an exception and die.
I'm not quite sure what the best way to approach this is but maybe send the bad ACL to another queue. A "reaper" agent could then save the messages.
Another possibility is to use the Dead Letter Exchanges which would tie Smith to rabbitmq but that's probably a given these days due to the amqp bindings.