I hadn't given this "tweaking reality" thinking much time until I read this thread - but it's an interesting one.
My own layout - a simple single track, single platform through station, with a small goods yard, on a now long-gone branch line. At a specific period of time, be it pre-Grouping, Grouping, early BR or Modernisation Plan BR, trains would have been few, and most would have been similar locos & stock. Pretty boring to the average person, I suggest. However, by running an assortment of trains that would have been seen on the line throughout its life, some of which were real oddball one-off workings, I hope to keep viewers entertained, especially as time between trains will be compressed. Who knows what we will see next? An early DMU? A pre-Grouping train, all ornately lined out locomotive with matching gleaming stock? A work-worn goods loco pottering about with the weekly pickup goods? Let's wait & find out...
The other compromise, of course, is that the station itself, with associated detailing, can't easily be switched between time periods, so the trick here is to have the little cameos for folk to see, and have it looking interesting enough to be more than a simple backdrop to the trains.
Will it work? We certainly think that it does for us, so hopefully viewers will too. We'll find out in February...
Mark