Omnigraffle pro and text

Is there a way to have any new item added (I use the outline panel) have a
new font size?

I created an omnigraffle pro document and added an outline - I also applied
one of the diagram styles.  It was set to 15pt.  I selected all objects and
set the font size to 12 pt.  Works great.

But every time I add a new object, it is back to the 15pt. Any way to make a
global change?