In this post Kirupa Chinnathambi demonstrates how to use ChangePropertyAction.
While customizing properties is something Expression Blend allows you to shine at, its influence doesn’t go beyond the artboard. If you want to change the properties of something in a running application, you probably have to write some code or do some other tasks that you may not like.
To make it easier for you to change properties at runtime, we created a simple behavior called ChangePropertyAction.