I do not believe it is possible to run an update action to enable/disable a watch using an Event procedure.
The following is the syntax rule for the update action command:
update action=action_code [watch=watch_id] [mh=modelhandle] [index=index,[attr=attr_id],type=attr_desc_type,val=value ...]
Notice you need to specify the action code watch id and model handle. In the Event procedure, I do not believe you can specify the watch id.
In the procedure, you specify the action code, model handle and some attribute values but there is nowhere to specify the watch id.
Joe