Hello,
I presume your workflow includes CAB approval tasks? You could code a 'behaviour' for the Pending status that looks at the CO risk and sets the task status to Skip the task if the risk is low (judging from what you write above, you may have attempted that already?). How are you launching the notifications? Presumably they're going out when the task turns Pending - which it always will. It may help if you add a longer delay to allow other behaviours time to complete, and in the condition test whether the task is still pending. Alternatively you could add the notification to the same 'behaviour' that decides whether or not to Skip the task. In that case you will have to use a Multiple Notification macro to send the notification, rather than an Activity Notification.
Hope that gives you some ideas! Please attach some screenshots of your task and behaviour definitions if you'd like some more detailed feedback.
Regards,
James