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. :-)
I added Disable field. The value of disabled field saved as "on/off" but I want to value of disabled save as "true/false".
There's likely a way to achieve this, but if you change the value(s) of a predefined properties you might break this functionality.
As far as I know the OOTB have the feature of required but no disable feature, did you add custom disablefield?