It just got me thinking - it's all very well saying to the guard that I'm only going as far as "X" today but I didn't know that at the time - and, in any event even if he did mark it, I would not think twice about breaking my journey and continuing another day with said mark (because they don't ever seem to mean anything) but it was as if the ticket had been fully cancelled.
It's normally been my experience that if I'm on a train that doesn't serve the destination station on the ticket (meaning the guard knows I'll have to change), they confirm with me which station I'm going to on this particular train and then mark the ticket accordingly.
The behaviour you've described seems very odd, as you were always going to have to change in order to get to Rye. It doesn't matter if you were going to continue your journey straight away or in a fortnight's time - your ticket might have been checked by somebody else at Hastings or Rye or at some point between the two, and they would obviously want to see the expiry date. And if there were any holes or marks on the ticket, then presumably they'd ideally want to satisfy themselves that those were made at an earlier point on your route and so do not indicate that you're trying to re-use the ticket. So it would have helped if the markings were legible and didn't obscure anything printed on the ticket.
I'm still not looking forward to being compelled to use e-tickets or bogroll tickets for this sort of journey, particularly if I wish to break my journey at a station that doesn't have ticket barriers.
I fear the act of the guard scanning the ticket before the break of journey will be interpreted by the machines (and even some of the people) that scan the ticket subsequently, when I come to use the remaining validity (particularly if it's on a different day), as tantamount to the guard having drawn all over it and deleted the expiry date as you've described. At best.
At worst I worry it could be treated as tantamount to the guard having ripped the ticket in half.