The options warbrand2 suggested are all nice and dandy, but not sure how to feel about most of them. It all comes down to the questions that what is a vanilla campaign/quick match customization option and what is a mod.

In the end, customization options provided in-game would actually be just mods created by us, or an in-game mod generator if you will. As the game is so open in how resources are handled, it becomes difficult to say how much effort should we put in UI work for mod generation as it's possible for the player community to come up with all sorts of gameplay settings themselves and share them by packaging them as overlays. The time spent by us working on the mod generator would be better used in creating new gameplay features, in my opinion.

Any UI provided by the in-game customization options would never reach the flexibility of mods obviously, unless we just add a text editor and a file browser in-game and tell you that's the option customizer. I'm sure anyone would say that doesn't make sense as you already have notepad and Windows Explorer in your system anyway.