There is NO practical way to move Part files, Assemblies or otherwise, from newer numerical release of NX to an older numerical release without losing both Parametrics and Constraints. The best that you can do is to move 'history-free' solid/surface models using the...
File -> Export -> Parasolid...
...function and selecting the desired target release and then doing an Open-As using this newly exported Parasolid file in the older release.
John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA