Any ideas of the cheapest way to split tickets / get cheaper fare for the 07.40 or similar tomorrow morning?
0740 from York should get you to Moses Gate at 0942, so I assume you need to get there about that time. Cheapest through fare at that time is £34.60 SOR (£22.85 with Railcard) or £24.10 SDS (£15.90 with Railcard).
The restriction on the £28.10 SVR (£18.55 with Railcard) is "
trains are barred which are due to arrive in Manchester (Deansgate, Piccadilly, Oxford Road or Victoria) before 0930." and I assume you need to arrive at Moses Gate before the first trains on which a SVR ticket is valid (York 0840 - 1005 Manchester Pic 1016 - 1032 Bolton 1039 - 1042 Moses Gate).
You could consider leaving York earlier to travel to Bolton by a slower, but cheaper, route. For example, one of:
0613 York - 0814 Blackburn 0832 - 0902 Bolton
0706 York - 0914 Blackburn 0931 - 1000 Bolton
Unfortunately there are no sensible connections from Bolton to Moses Gate from these trains, so it may be necessary to complete your journey by bus or taxi. Bolton and Moses Gate stations are less than 2 miles apart.
The best fares I can find for this route are
York - Entwistle route Burnley SDS £17.60 (R/c £12 min), SDR £18.90 (R/c £12.50), SOR £20.60 (R/c £13.60)
Entwistle - Bolton SDS £2.90 SDR £3.40.