Android : Way To Download / Replace Droid Resource Files?

My application will have some customisation for each company that uses it. Up until now, I have been loading images and strings from resource files. The idea is that the default resources will be distributed with the application and company specific resources will be loaded from our server after they click on a link from an email to launch the initialisation intent. Does anyone know how to replace resource files? I would really like to keep using resource files to avoid rewriting a lot of code/XML. I would distribute the application from our own server, rather than through the app store, so that we could have one version per company, but unfortunately this will give quite nasty security warnings that would concern our customers.