Checking if Virtual Server disabled within iRule

You can disable pool member instances without it impacting other instances. In other words, two different pools - but same pool members - for each virtual server (let's call them "test" and "prod" respectively). Manually disable the pool member's in the pool associated with the "prod" virtual server; the members in the pool associated with the "test" virtual server are not impacted and still show available in that pool. This effectively disables the "prod" virtual server without preventing it from accepting connections, and allows your iRule to work its magic. Your "test" virtual server is not impacted.