ANDROID_ID changes once signing key changed, but does the signing key change by a system update?

Question

At this Android Developers link it is stated that

The value of ANDROID_ID does not change even if a system update causes the package signing key to change .

Can a system update change an app's package signing key? And if so, how?

Answer 1

The only way a system update could change a package's signing key is if that package is in the system image. A normal app (that is, one downloaded from the app store that is not part of the system image) would not have its signing key changed.

That is to say: a system update, without a factory reset or a reinstall of the app, will not change the app's ANDROID_ID, and it won't change the signing key either, except possibly if that app is included with the system image.