I have a similar situation coming up, also for a genuine reason. I'm booked on an Advance Newcastle to Liverpool South Parkway on a Friday, changing at Man Vic (walk to Man Picc), and intended to return to Hereford on the next day, a Saturday. However given WMR's recent track record on Saturday services between Birmingham and Hereford, I decided it made more sense to come back directly on the Friday, as they seem to be a bit more reliable on weekdays.
As there is a 10 minute dwell at MCV, where I would have to leave the train for my connection anyway, I bought another ticket MCV-Lime Street, staying on the same TPE train, and a further ticket LIV-HFD via BHM. As I'd be leaving the train anyway, I'm hoping I can get away with re-boarding (my reservations are from coach C to coach A), and present my new ticket to complete the journey to LIV.
As I will have valid(?) tickets covering the entire journey, can I just present my MCV-LIV ticket if asked, as although I would have theoretically short-finished on the original ticket, by then it's history so they can't really retrospectively accuse me of anything? Does anyone know if TPE change crew at MCV on this route, which would be ideal in my situation?