First of all, there is no known way to switch off the front position light : it remains on as long as the bike is switched on (as the rear postion light).
Then, here are the three different headlight behaviours that I've noticed :
1 - standard behaviour : you switch on the bike, the low beam is on. If you switch to high beam, the low beam switch off, and vice-versa.
2 - both beams on : you switch on the bike, the low beam is on. You pull the high beam pass switch for approx. 5 seconds, and you release it after the first beep. You are now in "both beams on" behaviour : the low beam remains on when you switch to high beam (more light, but more consumption).
3 - headlight off : coming from the step 2, you pull the high beam pass switch for approx. 5 seconds, and you release it after the first beep (or, coming from step 1, you pull the high beam pass switch until you hear a second beep). The headlight turns off (so do the headlight telltale on the dashboard), but the position light remains on. You can use the high beam pass switch to send a "flash" to the cars in front of you. If you switch to high beam, the headlight behaviour comes back to step 1.
Of course, everything is reset to standard behaviour if you switch off the bike.
Now, I would like to add a personal note about this : I've been driven motorbikes since almost 30 years, and half of it in the parisian suburb. I had a very serious accident at the beginning of my biker career (I was about to loose my left leg but, fortunately, it's still there !), and since then a few minor ones.
During all those years, I've learned that one of the main points to drive safely (with reasonnable speed) is to constantly ensure being seen by motorists. I let my low beam always on, I wear a yellow safety waistcoat (I know it's ridiculous, but my life is more important than my pride), and I would have put a blue flashing beacon on my helmet if I was allowed to ! So I strongly recommend to let the low beam on (and to wear a safety waistcoast), your life is more important than a few kilometers of range !
Drive safely, if you want to have the opportunity the enjoy your marvelous Vectrix for long ...