The narrative parameters file is the means by which holo-programs are edited. While on a holodeck or inside a holosuite, one can open the narrative parameters file verbally to change or continue writing the currently open program.
Tuvok once wrote a combat-training scenario known as Insurrection Alpha in order to simulate a mutiny by the Maquis members of USS Voyager's crew. He later abandoned the program when the threat of such a mutiny appeared less and less likely, but not before Seska found the program. Feeling betrayed, she altered it so the next time Tuvok opened the narrative parameters file, he would be trapped on the holodeck and forced to play out a scenario in which Voyager was set to torture him until she (or at least a hologram of herself) killed him. (VOY: "Worst Case Scenario")