ASM Global and URL Parameters

Just do not change the parameter level setting while Policy is not yet out of Learning. If you do not want to start the Learning process from a scratch, you'll have to wait for the Policy Builder (current Learning process) to finish. Only when the Policy is out of Learning, you can proceed by deleting all the learned Parameters, and manually redefining them yourself with the new parameter level setting.

As a side note, you do not really have to go as deep as learning all the parameters. My best advice is to not perform wildcards tightening on Parameters initially, and if you later encounter any specific requirements in regards to parameters, you can add a few exceptions. It's better to have a policy with 5 custom Parameters, and one Wildcard parameter instead of a Policy with 500 Parameters and no Wildcard parameter. Despite added complexity, the second option does not add any significant benefit to security but it will certainly add management overhead.