Not even. It's a judicial review so is challenging the procedure, not the result. Even if successful, the most that can happen is that Ravec have to reassess their decision. They could very well come to the same conclusion all over again. I'm no expert, but I can't see this producing the result Harry wants. Security decisions are under constant review. Even if they had stayed as working royals, their security arrangements might have been downgraded by now, as they have been for other royals. Round the clock armed security is a limited resource.
So much effort, expense and stress for so little potential gain. I really do think this is a combination of Harry's stupidity and his sense of grievance, both of which know no bounds.