Hi,
When you want to control wether a workflow is triggered or not you rarely try to influence the event triggering.
Instead you influence the event-->workflow part.
There are conditions SWB_COND where you can control this. What I ususally do is copy the BO add some extra (virtual) attributes delegate it and then use these attributes for controlling the workflow triggering.
In some cases a check function module is the way to go swe2 event-->linkage double click and type in your FM.
If in the end you really really want to influence the event triggering you can always add a check function module on the event with transaction SWEINST
Kind regards, Rob Dielemans