Once I tried to select a small group of cars and then copy and paste but didn't worked to me, maybe I did something wrong...
Anyway I had to go to RW_Tools to finish the job, so now when I want to create a long consist (+70 cars) I add some few cars (any one) then I use RW_Tools to duplicate as much as I want, and also to swap to different types or liveries, or load/unload them etc. It's not much fast, though is more flexible.
Who doesn't have dog, hunts with cat.