Thank you for your post. This setting can be changed indeed only on an active connection; to change it back you would need to have an active connection once again, or as you did install a clean software and drivers. I have forwarded your recommendation though so it may be taken into consideration on a future release.
I just ran into same problem as Bob. By selecting only 5GHz on a card that doesn't support it via the Enable Intel Connection Settings and couldn't recover through the Windows 8.1 UI or Intel's. I had to go trough a Windows Recovery which corrected this.
I'm running latest drivers for Intel 7260-N adapter and PROSet software 16.0,8.
For average Joe user, this would be challenging.
Thoughts on fixing this Intel?