How can I change my.policy at the end of a F5 hosted site?

The URI should only be /my.policy if in the middle of an access session evaluation, like bookmarking a site while you're on an APM logon page. Normally, if you access an APM-fronted application, APM will do an initial set of redirects to /my.policy, finish the policy, and then redirect to the originally-request URI. It wouldn't be impossible, but it would be non-trivial to change the /my.policy URI if users are in fact bookmarking on the logon screen.