The Swiss also bought 158 of them which served into the 1970's, renaming them as the G-13 (any designated G-13 definitely served with the Swiss).
The Soviets regunned them with their 76.2mm but otherwise kept them basically the same.
The Czechs converted some of theirs by replacing the gun with a flame thrower, although Hitler had ordered this conversion in November 1944 so it's unknown if the Czechs did it themselves, or just picked up a few which had already been done.
From what I can see though, it doesn't look like too many other alterations were made to the armament.
There is no indication I can find of Austria having any after the war (I suspect unkated confused them with Switzerland).
https://en.wikipedia.org/wiki/Hetzer
http://the.shadock.free.fr/Surviving_Hetzers_G13.pdf