I will try that when I can. Probably this weekend. But why would I be able to hit all the other F options? It's just f7 that doesn't work. I can hit f2 to get into the BIOS.
As for not updating the BIOS I'm not sure why Intel states that but that is contrary to what you should be doing. You should always update your BIOS as it contains stability and security fixes. I'd rather not run into any issues then wait until I run into one.
Also remember I have two of these and I was able to update the BIOS in the other NUC without an issue. Using the same keyboard by the way.
I looked at your intel link and it says there that after powering off the NUC and back on that it resets the USB optimization. I've turned it off quite a few times. I'm not sure if your suggestion will work.