Say that after a passenger learns of or views the flight plan, she opposes it (eg due to safety).
She could just refuse to board the flight and forfeit her ticket and costs, but are there less costly and dire and radical options? Despite being only a passenger, could she explain to the flight crew (plausibly via the cabin crew?) her reasons and thus request the reconsideration of the flight route?
Supplementary: I elucidate that I do NOT mean for her to compel or impress a specific route (replete with all the waypoints, VORs, etc...) upon the flight crew, but only a general concern for avoidance.
As an instantiation, if I were a passenger and had apprehended my flight to overfly Ukraine, even outside of the no-fly zone, then I'd remonstrate against it, in favor of a more northern one that would substantively avoid Ukraine.