I tried to figure out a way to easily changed the corner radius of rounded rectangles "ex post facto" a while back and was never able to come up with anything quick and easy.
Effect --> Stylize --> Round Corners. Of course the boxes should then be perfectly sharp cornered ones, so you may first need to run the replace with shape function first from the same menu.
This is really simple
Selet the rectangle
Go to Effects>Convert to Shape>Convert to Rounded Rectangle.
Choose 0 for the extra width and height and change the radius corners at will.
Wow, that is very simple, and it works on groups of rounded rectangles. Thanks for the info.
Brilliant, Mr. Z.