Slitherine

In a campaign, is it possible to increase/decrease the # of garrisons and/or reinforcements between battles?

Or is it all hard coded to be based on battle size?

The minimum garrison is scripted to follow the size of the next battle, but there is a much larger maximum that the player can use if he wants.

Reducing the minimum would simply make each battle easier than the last, which wouldn't be much fun, whether it is (sometimes) realistic or not. So the garrison mechanism is fairly fundamental in the historically-based campaigns where the battles don't get progressively larger - and sometimes, for historical reasons, get smaller.

Almost none of the game is "hard-coded" however, it is all in the scripts and you can mod this like anything else. (But following how the scripts work for this might be a challenge. I can't tell you a simple way to make whatever change you are seeking. The code for garrisons isn't something that was written with easy modding in mind, because in our view modding it would break the Campaign system).