What you are asking is really not the way to do things in WPF. Use MVVM to set properties (that are going to change). You end up with an object (ViewModel) that has properties that when changed will change the properties of the control in the UI that the property is bound to.
If you are bound to do what you ask you need to investigate reflection.
It seems that you want to create a line of code in a string and then execute it. To do this you should look into CodeDom.
I think what you are trying will in the long run not do you any good and the time to implement something like what you ask will be long and difficult