Changing an existing component

[jmcilhinney]

But what do you mean by "This may not provide all the functionality you need though." ?

Extension methods can only do so much. They are only methods, for a start. You can't add instance properties or events using extension methods. Also, while they are called as though they are members, they are implemented outside the class, not inside. As such, you have no access to protected members of the class.