GC issue Traincrew with a 'unit wire' early hours and then updated if any swaps occur. Not hard in the world of smartphones ... Genius Mobile also allows crews to check various information about their shift/trains, including formation.
This is probably a bit easier for GC as they only have a few units in use anyway.
Stock changes are quite common. Sometimes my diagram will say 313, and you get down to the platform and a 377 is sitting there or VV.
And as for being told in advance. The last direct train from Portsmouth to Brighton runs into Littlehampton then reverses. Southern often use this to swap units to get a unit to Brighton and thus Lover Walk. There have been a few times as conductor where I have worked this train and first I knew about it was a few mins after stopping at Littlehampton. Sometimes you get a call, sometimes not.
As for taking the ****, I'm still recovering from getting stuck in an intermediate cab on a 8 car 377 between Lewes and Falmer
Now that was a fun call to control.
Nothing like the dread as after you get all the footie fans on the train, do the bells, get the train away to turn round with your t-bar and the dread as it just spins in the lock. Doh!!!!
not only was the platform staff at Falmer told, but the driver by the signaller, so about 3 members of staff came to get me out.