I don't believe that's possible. You'll need to create another policy and assign it to that one computer. Don't make the mistake of thinking "edit policy on a single system" will only edit the policy on that system. You can accidently edit your default policy because of this. McAfee should correct the verbiage to say "edit policy assignment on a single system"
So make a new policy and assign it to the endpoint.
You can't edit the policy for single client, make a copy of the policy you want to edit and exclude/modify required and apply to the single client only.