Possibly a blanket ban on silly posts like yours is the way forward. NR deals with hundreds of trespass incidents every year and only a very small number have anything to do with steam tours.
There is a difference. For one, most trespass incidents are random. Foreigners unaware they can't cross the line to get to another platform, someone on the run from police or even to avoid being penalty fared (happens quite a bit at some stations) and of course potentially suicidal people. Lots of reasons but rarely predictable.
On the other hand, it seems that you have one train running that has tens, if not hundreds, of trespass incidents. Most of which are clearly going to be unreported, and even those captured in photos/video doesn't seem to lead to much either.
So, while you try and do everything to reduce trespass on a day by day basis, if you want to have an immediate impact then it would seem logical to focus first on the 'easy' cases and that does mean a review of specific services that are seemingly guaranteed to cause these problems.
It stands to reason that sooner or later something bad will happen.
I do wonder why the train itself doesn't have lots of cameras, with geolocation data, to capture these people and highlight the issues - but then I realised the operator wouldn't want to acknowledge the severity of the problem for obvious commercial reasons. So there's a strong incentive to turn a blind eye, despite the safety issues.