I've got an existing Android app, which requires some 3D gameplay on only one of the screens. I've also got a Unity project containing the code for this screen on the iPhone version of the game.
Ideally, I'd like to pull the Unity code into my Android build, but all the documentation I've seen discusses building right from Unity. Anybody have any suggestions on how to combine the two builds?
As you say, Unity currently does not support customization post-build time. You could of course decompile the .apk and embed the necessary files into your own project, but that's a really hacky solution.
Instead I would suggest you have a look at the plugin support; a lot of customization can actually be done there by adding your own code and resources. Unity 3.1 also ships with the main activity code open; it can be found under < Unity App Installation >/PlaybackEngines/AndroidPlayer/src.