1) the render2texture.dll doesn't overwrite anything. It's simply a new implementation of the render 2 texture feature.

2) If the plugin can't get loaded, you are doing something wrong. Maybe the plugin is in the wrong folder or you need to install something (if the plugin is created in Visual Studio you would have to install the Visual Studio Redistributable Package). But only Chris3D knows if there is something that needs to be installed.

3) I guess that the shadows won't work with extra edition because it has no render to texture which is essencial for shadow mapping.