I've seen people ask about this before, and the response has been that there doesn't seem to be a need to expose the code through the UI.
Here's a real-world example of why this would be very useful:
We're looking to switch installers from Visual Studio Installer to something more powerful. We already have multiple release versions on the market.
If AI exposed the code, I could easily match the codes to the existing project, making a seamless transition, and preventing multiple applications showing up in the Add/Remove Program list.
Yes, I can edit the AIP file manually, but this is a good example of why someone would need to do it in the real world.