Thre is no F class on that Flight. Nobody's BP will say F.
F cabin is for Diamonds and Full Fare C pax only. If the check in staff and lounge staff do their job properly you will neither have access to the F cabin nor the F lounge.
That's they way it is on NH and they are not rule benders. They don't want to make Diamonds grumpy.

The only exception to the "No Grumpy Diamonds" policy is the odd check-in policy where *gold is often allowed F check-in lines outside of Japan. It really bugs when I have to wait behind UA 1Ps flying Y when I'm confirmed F.

Of course this was before they diluted my benefits and made me a permanently grumpy DIA.

Let us know what happens.

Scho