Ok I discussed a similar mode of operation on another thread. In theory, it is possible to mod the game, providing we have some form of control over train instructions. However, the possibility of being able to detach a locomotive from its train and the have it re-attach comes down to persistence.
Persistence is something we call in the game industry as an object that remains in a given state no matter what the circumstances. This means that for Train Fever, a train must continue to exist whether it has a locomotive or not and from what I’ve seen to-date, I’ve not seen any evidence that a train is persistent in Train Fever.
Additionally, to have such operations as you describe would require a much more complex signalling system than is presently available, and perhaps possible. It would require a networking system for each signal as each signal would need to talk to its neighbouring signal and that talk to its neighbouring signal and so on. So that the signals know the position and state of each train on the railway network. Once you’re able to do that, you can then code some intelligence into the system so that trains without a locomotive can be stationed in sidings and even marshalled, so they can be protected by signals without affecting the operation and function of running trains.
