After looking through the forum, I couldn't find a reduced garrison script compatible for 4.3 so I decided to just do it myself. I made it very similar to the way HHB RGS works. Instead of an entire army popping up, it's only three units or five depending on the city.
Simply just place it in ...\kingdoms_grand_campaign_mod\data\world\maps\campaign\imperial_campaign and overwrite.
Back up your original campaign_script.txt just in case you might want to switch back.