I was able to compile my own modified version of the Android SDK by following the answer to this question: Configure eclipse to use my own Android SDK (framework.jar).
I imported this modified SDK in an Android Eclipse project. After doing so, I'm able to call methods that I added in the modified SDK at compilation time, but at run time the emulator throws a noSuchMethod exception.
I'm under the assumption that I also need to copy the system images generated after the compilation. I tried to copy the files in the folder system-images, and also modifying the build.prop file as in the question above, but had no success.
What am I missing?