Android - What happens when a signing key expires?

Question

If a signing key expires, do existing apks refuse to install, or does it just mean that new apps can\'t be signed with that key?

We are recommended to use keys that

Answer 1

If a signing key expires, do existing apks refuse to install, or does it just mean that new apps can't be signed with that key?

jarsigner will refuse to use an expired key, and apk's signed with the old key will be refused by Android on install, but apps already installed will continue to run just fine.

https://developer.android.com/guide/publishing/app-signing.html

If an apk's key has expired, is there any way of installing it (without relying on the developer to re-release)?

Yes, the apk can be resigned with your own certificate.