Visbits, maybe?
You know the messages that appear at the bottom of the screen sometimes in systems? I was wondering if it was possible to use visbits to create a system with one of those messages, used only for a specific mission. For example, the player would be sent to a system, but on arrival to that system, a message would display at the bottom of the screen telling the player to instead go somewhere else.
Come to think of it, it's used in a few missions in the stock scenario. Now my question is, how do you do it?