The radio buttons does the same thing. Adding tabs is more of a design change. Opening tab would perform the same functionality as the radio buttons do. Although having tabs in place of radio button is fine too.
Tabs can better hide some options: kerning is only relevant to text layout, so is text justification or waterfall.
I guess I misunderstood your earlier email. In that I was referring only to the drawing surface area. As far as options like you mentioned are considered I too think tabs would do better justification to the functionalities of each demo program.
Actually left layout of the interface would only be for options and wouldn't change as per the program instead some options might be disabled if not applicable to the particular chosen program but this will happen in the tab which would contain options mostly common to all. Separate tab would also be there for specific programs which would be triggered when testing a particular demo program.