Parasolid data is always stored in Metric units. There are NO options for English units. Even inside of an Inch units NX part file, the Parasolid data itself is stored in Metric units (actually in Meters, if you want to get technical).
To do what you are wishing to do, you should instead open a BLANK Inch units part and then "Import" the Parasolid model into it. NX will automatically handle getting the units correct for everyone concerned.
However, when you "Open" a Parasolid model directly, since we have no way of knowing from where it came, we had to pick a default set of units and since the vast majority of the world (including the majority of the NX user base) is using Metric units, we were safest assuming that the part was intended to be used in a Metric format.
John R. Baker, P.E.
Product "Evangelist"
NX Product Line
UGS Corp
Cypress, CA
Phone: 714-952-6032
FAX: 714-952-5758
John.R.Baker@ugs.com