Thanks for the usage example. That may come in useful at some point.

I know for a fact that it's possible to create the assassinate_general mission type in script. Have you tried using the character name instead of the label? Have you tried using the script command version of create_mission instead of the console command? I would also recommend making a new custom mission subtype for this and removing as many parameters as you can (they aren't needed if you're creating the mission in script).