I propose simplifying the replacing procedure. Instead of sending the vehicle to depot, and doing all that, there are 2 methods that can be used
1) Simply click the replace button on the train’s window, choose a new consist (new loco and wags) and click confirm, and the vehicle is magically replaced on the spot. (just like in locomotion)
2) The depot window provides an additional button “Replace trains”. Press this button, choose a train or more than one train,or an entire line. Then choose the vehicle for it to be replaced with. Click confirm. Now these vehicles are sold on the spot and new ones come out from depot.