Grandfather rights apply to the vehicle, its design and operating on the railway. So a older design is not governed. Y current TSI needs.I'm fairly sure that grandfather rights apply to the vehicle, rather than the design, otherwise you'd just keep building vehicles to older designs. Also, you seem fairly sure that making the door opening wider is simple, but after all, bunging diesel engines under 769s or D78s, or even installing the sliding doors into mk3s should have been simple...