Ericmopar wrote: ... Swapping engines in a pre existing scenario is more problematic without RW_Tools. 
Actually, engines can be swapped without resorting to editing files. 
1) In the TS Scenario Editor, navigate to the location of the engine you want to replace and locate the viewing camera so that you can see both the engine and its driver disk.
2) Place the engine you want to use instead as close to the engine you want to get rid of as possible, either on an adjacent track or directly in front of or behind that engine.
3) Move your mouse pointer over the driver disk until it is selected (the driver disk will change color or luminosity).
4) Press and hold the left mouse button (do not click: press and hold). 
5) 
Slowly and 
gently move the driver disk (all the other disks will move with it) until it is in position over the front end of the new engine. Release the mouse button.
6) Click on the old engine (now without any disks) to select it and press the Delete key or simply drag the engine to an area without track.
7) Click and hold on the new engine and move it into the old engine's position.
8) If the old engine was part of a train, be sure that the new one is coupled to that train.
This process can be a bit tricky and certainly requires a steady hand when moving the disks, especially if there are a lot of them, but it does work. If you make a mistake and the disks disappear, simply back out of the editor without saving and try again. Remember that if you are swapping a steam engine with a diesel or electric one you will have to either add or delete a tender. It's also a good idea to check the new engine's number and name in your scenario after swapping.