After Effects: Changing a Rounded Corner's Radius
COW Library : Adobe After Effects : Graham Quince : After Effects: Changing a Rounded Corner's Radius
Here's a really short, mythbusting tip. Recieved wisdom is that when drawing a rounded rectangle mask, once you let go, you can't change the radius. Turns out you can!
In this mini tutorial I cover changing the radius while drawing, altering it afterwards and also show how Shape Layers make this much easier than masks.