Remember when I talked about the ability to intercept application codes and tell the Windows Phone OS that my app is in fact some other app? It seemed to me like the actual use of these IDs is quite limited - after all, without the ability to install a XAP package automatically without the user knowing about it I can't do much. But it appears the the entire code story applies more to the remote part of the OS - the Marketplace, and not the local one.
So once you got an application code (or GUID, or AppID), you can plug it into the application manifest (that is not the application it claims to be). Now, given that the user has a Live account set up on an actual device, he has to do this:
1. Navigate to the Marketplace application
2. Search for the application the GUID actually belongs to
3. There it is - it can now be rated.
Once again - this doesn't seem to be a major problem because it is really slow when it comes to the actual implementation. In the first place - the user needs the application GUIDs (not a problem to get those through a Zune API query), then those GUIDs need to be passed to an application that will be installed on a physical device and then go through the entire rating process.
NOTE: In order to be rated, an application has to be installed on a physical device. As long as the GUID is registered in the Marketplace, the application will be recognized as a downloaded one and not sideloaded.