I needed to re-install an older Adobe AIR application to check whether it delivered the function I remembered, and ran into the "... installer file is damaged". Repackaging of Adobe AIR applications is not an option for the end-user. The second Workaround to manually launch "Adobe AIR Application Installer.exe” with the "ignoreExpiredCertificateTimestamp" option worked.
Having to launch the installer with Admin privileges seems to go against best security practices. I may elect to install an Adobe AIR application to a personal folder, which would not require any Admin privileges. A better solution would be to add an option to the Adobe AIR Installer so that the user can select whether to enforce or ignore expired certificate timestamps.