You're welcome ^^
zeneventd is the daemon that executes transforms as far as I know. When your transform crashes (python exception) you can see it in $ZENHOME/log/zeneventd.log. You can also try stopping zeneventd and starting it in debug mode (as zenoss user) :
zeneventd stop
zeneventd run -v10
As for changing an event class, I think it should be done via event mapping not transforms. If I understand your issue correctly, Zenoss considers your event having the main event class. Even if you change it via a transform, Zenoss shouldn't re-check for the new class' transfrom : that step is already done. But if you had mapped your event to the /Trap class, then your transform would have been activated. You should check Jane Curry's event management paper for event mapping. It's quite good !
Also, cascading event transforms might be of interest to you.
Good luck,