No. You are only able to change the shape on a diagram (via the stereotypes dialog or a profile). If you create an MDG Technology you can define the icon that will show on a toolbox page. That's it.
I've pushed for some way to change the graphic shown in the project browser and in package contents. No such luck. As of the most recent time I've had feedback from Sparx - just before 7.1 went to production - this was not in the list of intended changes.
Of course this might have changed, but Sparx has not suggested that to me.
My strong suggestion is that you make a feature request for this. Not just here in the forum, but to Sparx directly. You'll find the correct form by following the link near the bottom of any forum page. Perhaps if enough people ask for this it will get onto the list.
David
