Regarding the Class 80x PIS, one of the major shortcomings of what is mostly a pretty flexible system is that once a train has been loaded into the system, you can't then alter it for an early termination en-route. You can use a generic headcode if one exists for the revised termination point, or you can run without a code and lose seat reservation information. A generic headcode from the east ending at Bristol won't exist, so the only options would be to keep the original headcode with seat reservations loaded, or remove the headcode meaning manually selecting the doors at each station and have no screens, reservations or announcements. Usually it's best to keep it in the system and make manual announcements where necessary.
A software update allowing the final station stop to be removed, as you can do with intermediate stops, would be a good thing.