Custom health monitor

There is not a way within the built-in HTTP and ICMP monitors to specify additional parameters, and in this case I'd venture the alternatives would be different. For example, to inject some piece of data into a ping packet, I think you'd necessarily have to proxy it. Off the top of my head I'm not imagining what the iRule applied to that proxy would look like to do this, but I can say it probably wouldn't be trivial. For an HTTP monitor, I'd almost always recommend an external monitor. This basically shells out to a management plane process, for which you have the power to do just about anything you can think of, including accept parameters.