Hmm, did you try to right-click on the rift.cfg file and choose "open with" and then pick/browse to Notepad?
Another possibility is that Rift changed some paths for storing data a few patches back and the rift.cfg file in C:/PROGRAM FILES(X86)/Rift is not the one you can change
Look for the rift.cfg file here:
c:/users/your name/AppData/Roaming/Rift and same thing open or choose to open rift.cfg with Notepad
You are correct the file does reside in your profile but the config file in the Rift folder points to that file. The OP probably still had Rift open or for some reason still had a lock on the file even while closed. Reboot usually fixes it.
I am running an i7 3.6 processor, i have updated my nvidia 670 drivers, there are no viruses on my machine (ran malware antivirus etc.), I have looked at the Rift cfg file and it is already at zero, my machine is clean inside, and i ran the Heaven gpu benchmark tool for an hour with no problem. I also have auto update drivers turned off for my gpu to avoid win 10 conflicts. And i ran a hardware scan tool that did not detect anything amiss. I also have GPU-z and i ran it while killing monsters around Lantern Hook i get screen crashes at only 77 degrees. The game crashes at least once an hour on this machine and it is getting more and more annoying. What else can i do?
Regarding drivers: Windows should be updating drivers when it spots new ones, whichever vendor your graphics card is from should have come with some bundled software and it should be also alerting you to any new available drivers, e.g. Nvida Geforce experience software.
If those don't quite do it then its worth trying some other software like Glary utilities or similar that can interrogate the system and identify any out of date drivers.
It's less likely to be a driver issue, unless you have never permitted automatic updates, ever...