You need to use the UI Framework and Mod Configuration tool mods. At the start of a campaign, it will let you alter spawn values.

When playing as Chaos, the "Gates of Chaos" values should be set to minimum for both army size and chance in order to avoid making the game trivially easy. Minimum values provide variety and wildcards without being cheesy. Even at a 2% spawn rate, I still see an army pop up every 40 turns or so. It also comes out laughably weak and must survive as a baby chaos army that you can choose to protect or let die.

Baby chaos vassels can also cause you pain if they anger too many other factions by raiding them, who will then delcare war on you as the master of the vassels. On the other hand, vassel choas armies do provide a decent side income and will always stay allied to you. The tradeoffs work both ways.

You can see how I use all my mods together if you look at my collection list for best gameplay mods.