What you are looking for as Sahisahi did mention is CurrentExpansion.cs.
https://github.com/Grimoric/RUNUO/blob/master/devel/Scripts/Misc/CurrentExpansion.cs
Line 8: private static readonly Expansion Expansion = Expansion.HS;
This can be set to None, T2A, UOR, UOR, UOTD, LBR, AOS, SE, ML, SA...