I think the original question was to depart at night with a Inop Nav light?
This was on the ground prior to departure, possibly discovered on the preflight walk around, I presume.
In flight it is normal to continue, unless someone informs that the light is inop, other traffic ATC etc, you would never know anyway, even then I have never known anyone to turn back or not to continue.
.
As far as before departure it would probably take a waiver or permit from the FAA or CAA what ever the case may be.
No other local governing regulations less than the FAA or CAA can override the manufacturers MEL/ DDPG.
I doubt they would issue one anyway, they would just tell you to fix the light.
Be careful though as in some aircraft the second bulb will not work until the anti collision light is on.
This is Ok to depart and complies with the regs.
Hope this helps.