If the trains both call at Northallerton & Huddersfield, then I agree there is no difference in this respect.It's on a Friday. I've previously been told to change at Northallerton for the same reason. Is this correct.
However if I had a decent seat I'd prefer to remain in it as long as possible, and it's also perhaps better to make the change as late as possible as you have more onward alternative options if things go wrong.
I don't think any journey planners look at platforming?Just out of curiosity why do itinerary planners state York as a change point on this route when at Leeds is a same platform interchange and the platforms are predicted in advance?
If it's an Advance ticket, then it could be argued that it's technically 'mandatory' to change at the point where you are required to change. In practice, no-one's going to say your ticket is invalid as a result. Your seat reservation won't be enforceable of course as once the train has left York and remains unclaimed, it's free for anyone to sit in.Regarding the change at York. Is this mandatory or can I change at Leeds? Real time trains shows both trains at platform 16A at Leeds whereas its platform 3 arrival at York and 9 departure. Obviously this could change I know.
If you want to select your own interchange point, book the ticket at your local station (or telesales).