Do I understand you correctly, that you want to extend the "settings dialog" (don't know it's offical name right now) on the right hand sind (you marked it with a red box)? What kind kind of property do you want to add? And why you would do it is also an interesting question. 🙂
There's likely a way to achieve this, but if you change the value(s) of a predefined properties you might break this functionality.