I've tested here on my Tumbleweed system, using a dummy package to echo output
messages. It's working for transfiletriggerin but, sadly, it gets invoked way
too frequently IMO.
In a DUP transaction with 377 updates, transfiletriggerin got invoked around 76
times. And transfiletriggerpostun still no joy.
> $ rpm -q rpm
> rpm-4.17.1.1-2.1.x86_64