At this point a nuclear power like France has no issue with using covert violence to produce compliance from Musk and he must know it.
These people have proven themselves to be existential threats to French security and France will do whatever they feel is necessary to neutralize that threat.
Musk is free to ignore French rule of law if he wants to risk being involved in an airplane accident that will have rumours and conspiracies swirling around it long after he’s dead and his body is strewn all over the ocean somewhere.
The second Donald Trump threatened to invade a nation allied with France is the second anyone who works with Trump became a legitimate military target.
Like a cruel child dismembering a spider one limb at a time France and other nations around the world will meticulously destroy whatever resources people like Musk have and the influence it gives him over their countries.
If Musk displays a sufficient level of resistance to these actions the French will simply assassinate him.
It's just that the West has avoided to do that to each other because they were all essentially allied until recently and because the political implications were deemed too severe.
I don't think however France has anything to win by doing it or has any interest whatsoever and I doubt there's a legal framework the French government can or want to exploit to conduct something like that legally (like calling something an emergency situation or a terrorist group, for example).
Why not? After all, that's in vogue today. Trump is ignoring all the international agreements and rules, so why should others follow them?
PS Yes, Greenpeace is a bunch of scientifically-illiterate fools who have caused far more damage than they prevented. Doesn't matter because what France did was still clearly against the law.
OpenDNS is censored in France... so imagine
Seriously, every powerful state engages in state terrorism from time to time because they can, and the embarrassment of discovery is weighed against the benefit of eliminating a problem. France is no exception : https://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior