Unable to edit ASM Policy while Auto Detecting Application Language

Yes, this is expected behavior that you are observing. Anything you configure within the policy is dictated by the application encoding language being used and it is how ASM parses through the request as well. With automatic learning enabled, you are leaving it to the policy builder to learn the language used by the application and make the decision. Alternatively, you can set the application encoding language manually. Once the language is selected, you cannot modify it again within this policy. You will have to re-deploy the policy, in that scenario.