Hi Minnow,
EA's take on modelling-related adaptations (ie stereotypes and diagram toolboxes) is that you should model those as well. Kinda neat in its way.
As long as you don't need the elements to be displayed any differently in the diagrams, you won't have to write any code, just develop the model that describes your adaptation, push it through the wizard and you're done.
If you do need your elements to look different in diagrams, you have to write some code in EA's ShapeScript language. Not too bad, really. If you only need your element symbols to be different in the diagram toolbox, again, no coding needed.
The other thing with EA is that it's a modelling tool, not a drawing tool. This is reflected in the adaptation design philosophy: you can't just create a different skin for an element, you must actually make decisions on the metamodel level.
So I don't think your suggestion will get much traction. However, creating a UML profile and a custom toolbox is a pretty straightforward process and there's plenty of info in the help file.
Failing that, there are always consultants around who will gladly build your adaptation for you, such as Geert or myself.

/Uffe