Re: Corner Effects
Create the rectangle with the corners rounded. Then, with only the rectangle selected, choose Object > Paths > Close Path. This will convert it to a generic editable vector object. Each corner will have two points, one of which is a "corner" point, and one which has a bezier curve control point. For each corner of the rectangle you want to make square, select the point that has the curve control point using the "direct selection tool" (the white arrow) and note its X or Y coordinate in the control palette. Then select the other point for that corner and change the X or Y coordinate to match. You will no longer be able to change the corner radius with the corner effects setting.