Ideally, you should have an F5 BigIP in your (production parallel) staging environment. This allows you to test new configuration, code versions, features, etc without impacting production.
Assuming that this is not possible due to cost or other constraints, then the next best alternative would be to have a second set of 'QA' or 'UAT' services that is configured to hit the same back-end servers as production, but only has a small fraction of users targetting it.
Without knowing more about your configuration, it's difficult to be more specific. Are you able to provide a bit more detail as to how you are using your load-balancer, and what changes you are planning to make?
UPDATE: based on your clarification, it seems that you want to test your ability to flip users between one set of back-end servers and another, and that you are routing user requests based on the URL they are accessing? (Content switching).
If you are unable to afford another load-balancer in production, I would suggest configuring a new service using a test URL, and forwarding the requests to that URL the same as you do in production currently. Once you are happy that this test service is working as per production, you can change the policy associated with the test URL to forward to your new backend. This should verify that your Big-IP configuration is correct.
(Apologies for the lack of sample configuration, I've not worked with F5 load-balancers myself, only other vendors.)