Have NX Update the Weight Data on Save
Per-Part setting:
Start NX -> Open a file -> File -> Properties -> Weight (tab) -> Update Data on Save (check box) Toggle it on and apply/ok the dialog.
This setting is per-part, so you’ll need to do this for each part you want the weight data updated on save or set your user preference as the default.
User/Site/Group default setting:
Start NX -> File -> Utilities -> Customer Defaults -> Analysis (section) -> Weight Management (sub section) -> Generate Weight Data (toggle)
The next time you save, the weight data will update. Or you can force the update witht he button on the dialog.