I don't think you can disable that feature that was added as a security requirement.
What you could do for the Guest operator logons, is modify the skin and add some style code to hide the section so users will not see it. For the ClearPass Guest Skin you can add the following code in the HTML header:
{literal}
<style>
.contentTitle{ display: none; }
</style>
{/literal}
Hiding this message could make the solution less compliant to security requirements.
If you need the message disabled in Policy Manager and Insight, I think it is best to work with your partner or Aruba SE to raise a feature request to make that message switchable.