Thanks to Shane and Andy who quickly got me in the right direction and Bernie who pointed out the PTC problems.
The file name is "creo_parametric_customization.ui" or "creo_parametric_admin_customization.ui" The location is, well, not very well defined.
My customization file happened to be in my .wf folder which is where PDMLINK stores it's local cache stuff. That's the reason I lost it, as I had expected, because I had deleted my .wf folder due to a local cache problem.
The file can also be located in your loadpoint/text folder, your start-in directory, or as Bernie pointed out, in any folder you set as working directory because once you change directories, CREO wants to store it in the current working directory. This will create multiple copies. Fortunately I am in PDMLink so I generally don't have to change directories.
I am going to move mine in to the start-in directory where my personal config.pro is so it makes sense to me.
Thanks for the quick responses.
Steve Williams Pro/E Version 15/16 (Circa 1995/1996)