I'm really not following your angle, here... why do they need this flexibility to run a simulated service with no passengers?
I'm not seeing the unions killing anything. I'm seeing that it makes no sense to change the shifts someone works one week for no other reason than to allow some managers to Stand By And Sternly Observe for the first day. As I said in a previous post, they've already been running test trains for several years now, there's just going to be more of them. If an emergency should manifest, or if they are that nosy, then the suits can rush down there ad hoc. Otherwise there would be no service outside of the 9-5 hours at all.