Problem making a "Developer Tools" like program.

Question

Hello Guys,

  I'm currently developing a new program using C# and WPF. I'm trying to allow the user to be able to open a webpage and have the program automatically read and change the HTML page / code. Since I'm using WPF I hade to use something called MahApps.Metro that make the window look all windows8 like and that kind of has a glitch with the Web Browser control in Visual Studio. So, I simply decided to open the users Default browser to a specific page, but I can't seem to find anywhere where to actually change the HTML in the actual webpage without using the built in "Developer Tools" for the browser (Chrome or IE9). Does anyone know how to do this?

 

     PS: I don't mean changing the actual page, but changing the page on the computer side..Like what the "Developer Tools" in Browsers do.