[This is preliminary documentation and subject to change.]
Changes the Lead locomotive (i.e. the loco which the player controls) to the next in the consist. Steps back through the train, ignoring any cabs that face rearwards until there are no forward-facing cabs left. Then continues from the rearmost, rearward-facing cab, reverses the train and resumes stepping back. E.g. if consist is made of 3 cars, each with front and rear-facing cabs (A-b]:(C-d]:[e-F) then pressing Ctrl+E cycles the cabs in the sequence A -> b -> C -> d -> e -> F