They are two separate tickets. Preston to Manchester on an Off-Peak Return and then Piccadilly to Euston on an Advance Single. The Preston to MCR ticket bought on here does say on the details an arrival time in Piccadilly, so I assume implicit in that is that I can break the journey before Piccadilly. The reason for asking here is there are often RPIs at Deansgate and I would like to know how to respond if they say I can’t rejoin to Piccadilly.
Depending where you'd be on Deansgate the best bet may be to take a tram or the free city centre bus to Piccadilly. A single from Deansgate to Piccadilly is an outrageous £3 (unjustifiably high, but maybe deliberately so to discourage its use for short faring given few will be sold?) so this is probably not recommended.
Knowing the competence (or lack thereof) and pettiness of Northern's RPIs and prosecutions department this is not one I would attempt to argue even if it technically is valid to do this. It's not worth a tram fare (or a free bus ride) to me to deal with any resulting hassle.
Ending at Deansgate would be OK on a walk up fare whether break of journey was OK or not as it is a member of Manchester Stations. I have however looked and BoJ is permitted on that fare.
