I for a while was under the impression that the timetable mode was a kind of structured free roam. Boy was I wrong. You can’t do any thing that you want, and I really want to be able to do shunting without being kept to schedules. Please add a free roam mode like Train Simulators with no AI to get in the way and the ability to do whatever at your accord.
Some ideas about how free roam might work in terms of game mechanics: https://forums.dovetailgames.com/threads/thoughts-on-tsw-2020.17191/#post-87940
Or the ai that terminates (for example) Reading or London Paddington, you can take over the service and drive it. And when you want to stop driving the train it will automatically turn into ai