Is this possible? And how about louder noises between cars? I think hearing a diesel as a passenger would be cool.
Yes, you can do it, though it requires some imagination to make it happen in game. I had to intercept an AI train, stop it, remove the electric locomotive and then put the Geep the on the back. It's a bit frustrating with TSW being the way it is at the moment. MSTS, Trainz and Railworks allowed users to run their trains in whatever consist they wanted and on whichever route they wanted, yet TSW does not permit this. I bought the GP40-2 DLC with the expectation that I'd be able to use it on future routes, but unfortunately it seems that the existing content is locked to the route it comes with, therefor I can't drive the GP40-2 on the NEC route; This absent element seems like a backwards step in the context of train simulation.
You should be seeing the GP40-2 in service mode. The game is designed to switch it in to replace some of the GP38s.
When I go to the Service Mode the locomotive filter only shows the ACS-64 and walking as options, I don't even get the GP38-2 for NEC. This is what I see:
That's because the freight schedule for service mode isn't finished yet. You can spawn in walking to the freight yards and essentially do all of the switching \ movements you want because a lot of the freight yards and tracks between them are using manual points and are without signals. You'll find the GP38-2 and GP40-2 sitting in various yards, as well as freight cars. The developers wanted to add in a more involved and busy freight schedule but weren't able to finish it in time for release. It's incoming though.
Derailing a loco in the New York Switcher scenario causes signals to be disabled instead of terminating the scenario.
After that i just collected some Amfleet coaches and went all the way to Newark Liberty International Airport.