The AI player trains obviously change their manifests as it suits them. After you've bought out the AI player, the trains you inherit continue to automatically change their manifests as long as you don't mess with them yourself.
I'm hoping for some way to enable that for my own trains. This would be especially desirable near the endgame when I've got craploads of trains all over the map.
rupert, you've suggested 'Micro Management'. Either you meant I can go on micromanaging my own trains (undesirable) or that's a configurable option that I can't find. eriador suggested you indeed meant the former, which I specified in my first post I was not looking for.
It is my single biggest annoyance in the game, besides the crashing (typically just graphics related as of 1.0.1.0) of course.