Your mileage may vary ... When I originally installed CS6 on my new PC with a GTX 670 card I had to go edit the cuda_supported_cards.txt file and add the card; plus tweak the Nvidia settings (see link below). Anyway, tonight after I installed the 6.03 patch update I had to modify the file again. But I could not get notepad to save the file without an access denied error. Even though I installed the original program and patch update under my user name with administrator priveleges, I had to go back and run notepad as administrator. Just an FYI post in case someone runs into this issue.
Another tip is to keep a copy of that file in My Documents. With every Adobe update, you then just copy that file back over to the Premiere Pro folder.
If you drag the txt file on to the desktop, you can normally edit and save it without problem, then drag it back. Keep a copy elswhere for the future, as Jim says.
You don't need to edit the file to recognize your card, simply delete the file and hardware MPE will be enabled! That's much easier.