In theory, this is possible. However, the more elegant way to do it concerns creating a few additional assemblies - one responsible for RadControls, one responsible for the standard controls, and one for the interface that all controls should implement. Finally, you can load the assemblies responsible for the controls dynamically in your application and depending on which assembly is loaded, your application will provide different UI.
Please note that whatever approach you take to deploy your application, in case the assemblies are not merged with the executable of this application, you should build them as described here.
Feel free to modify the provided solution according to your specific needs.
All the best,
the Telerik team