i might be wrong, but i believe that you are mixing 2 things.

When zenoss monitors a device ( that you added manually or in the mass discover), zenoss is the one ASKING the devices.
In that case, when it sees a problem, it creates the event, and when the problem goes away, it is cleared.

If a device SENDS traps, it can be added to zenoss or not.

In this case, you have to see the events generated by the traps, reclasify them (maybe into an existing class, or to one you create), and then you can add transforms to them. I guess the "clear" trap should have a transform for clearing the other one.

I am new too, so that is the most i can give you, but with examples, i might be able to research more. (i myself only reclasified events sent from a storage, and used a super simple transform to set the message or similar to text the trap sent).