Greetings, Andrew,
There is a way to load inventory records into IFS Apps 10 using the Migration Job functionality (nav path: Solution Manager > Data Management > Data Migration > Migration Job). There you can create a new job and configure to suit your import preferences, as well as create the data mapping to match the import file to the IFS view (in this case INVENTORY_PART_IN_STOCK) where the data will reside. Remember to fully qualify the inventory part with config ID, lot/batch, serial, Eng Change Lev, and W/D/R. There is a column for PART_OWNERSHIP and OWNING_CUSTOMER_NO.
There are a couple of things that I would caution you about: this job does not create an inventory transaction, for example the NREC you referenced above, which may not be a problem during a upgrade migration, but may cause auditing issue during normal operations. And as I mentioned before, don’t forget to fully qualify the inventory part, as you might overwrite existing records depending on the migration job Procedure Name chosen.