I've been trying to do the same thing. We work our prototypes until we come to a design platau. Our billing Dept. then assigns a part number for general use. I found that I too could change part numbers but could only go so far. I then read,
"If the active project is set to shared or semi-isolated, you cannot edit the iProperties on a file that is checked out to someone else or on the workgroup version of the file."(bold & italics mine)
If the file is refferanced....hmmm... I closed the file, infact I closed Inventor and opened Design Assistant outside of Inventor. As I had my prototype in a separate folder, I simply opened the folder and had access to all the files. There I found the files I had renamed and with a right click on the file I opened iproperties, engaged the Project tab and had the old part number splayed out and ready to fillet. The cancerous old number was then excised.
The surgery was a success and the patient "IS ALIVE" (BWAH- HA HA- HA HA)!
Forgive please, this issue has driven me to a madness DEMANDING release. If you found this post you know what I am talking about. Now,... it is time to eat cake....yummy are the fruit of ones labor.
-palmhat