I don't think it's possible, but if it is, and someone knows how to do it, do tell.
Other way around. What do you want to do? There might be a better way.
And if you're deadset on rotating explain it better. Do you want the train to follow a circle or do you want it to turn around it's axis?
I want it to rotate on it's axis.
I.E.,
I want a train that goes on one of those platforms that spins it and it then goes on another route
-or-
I want a transport shuttle that turns around when it reaches it's destination so it won't be going backwards to get back to the original pickup location.
The only way to do that is so complicated (designing the train in a specific way which allows its parts to turn independantly and giving each part its own path) that you're better off designing a train to look like it could go each way.
You could do it with mapscripts, but that'd be tricky to get it right.
Much easier to just make it stop, and go backwards.