As Darkest Hour runs on ancient software it's very hard to mod in deep changes to its political and economic mechanics, which are built for railroaded rather than dynamic movement. They're not like HoI 3 where faction alignment and political party popularity are handed through charts and graphs. Nonetheless small things like ministers, flags, tech teams, etc. are trivial to change and some mods achieve a lot by adding a large number of events. Through events it's even possible to have context-specific negotiations through complex branched event chains with multiple possible outcomes.