The interface, where you find button and how you set things are different. I'm not sure whether the IGES, STEP or DXF underlying translators have changed, so that you would want to apply different settings as a result of improvements you might do better to take advantage of.
The .def files themselves are just an ACSII text collection of settings as far as I can see, so it shouldn't matter if you select a .def file created from an earlier version of NX. It isn't very hard to test this or print out the contents to compare.
Cheers
Hudson