I've been looking into this further, and whilst the VBScript approach would update existing elements, what I really want to do is this and ensure that any future Message element created automatically has the Tags I want.
I've been reading the help file, and found that there is a feature where I can Synchronise Stereotypes. The help for this says :-
"When you create an element, attribute, operation or connector from a profiled object, the Tagged Values and constraints are added from the Profile stereotype. Subsequently, you might update the constraints or Tagged Values of a particular stereotype in the Profile, in which case the items already created in the model would not have those additional constraints or Tagged Value tags and notes."
"You can apply the updated or missing Tagged Values and constraints using the Synchronize Stereotype function. This operates on any profiled element in your model, from any technology that is integrated with or imported into Enterprise Architect."
Now, this sounds like just what I want in that it will add the tags to all existing Message elements, and also, when I create new ones, add the tags to these as well.
However, I cannot find a way to modify the standard Message (in the BPMN 2 toolbox) to add the three tags I want. I don't understand the help as it talks of editing the Profile. Where do I find the Profile for the Message element and how then do I edit it to add the Tags I want ?
I've spent a good few hours looking, but without success (I have tried the Profile toolbox, but I didn't understand it or do the right thing) , so I am now hoping that my Sparxian experts will point me in the right direction !