You irule is correct but you have to understand why your irule is not working.
In your case you have to enable Oneconnect profile in your VS. The problem is when you trigged another URL and you have to pass trough another pool it can not work because you have a connection attached to the intial pool. OneConnect allow to detach connection for each request:
When OneConnect is enabled, the BIG-IP system maintains established connections to pool members. This allows the system to use established idle connections on the server side to load balance individual client requests from the same client-side connection. A server response tells the BIG-IP system to detach the client-side connection from the server-side connection. This allows the BIG-IP system to select another idle server-side connection to load balance a subsequent request from the client. The known issue prevents the BIG-IP system from detaching the client-side connection when it receives a server response other than an HTTP 200 status code. This disables request-based load balancing.
For this need the best solution is to used LTM Policy as describe by sajid. LTM policy is processed by request sor you will not have the problem that you meet.
