@mjg59 When I took the train to Ukraine (in the before times, when the war was just simmering in the East) there was a more old fashioned change of gauge at Przemyśl.
They lifted each carriage up on jacks and changed the wheels, while we sat on board getting our papers stamped. There's a yard of spare wheels of both guages for them to draw from.
Not a fast process, lifting one carriage at a time. I think it took well over an hour...