How do I change castle tower appearances?

I want the towers for my Northern European fortresses to look like citadel towers - no roofs on their tops.

I've tried deleting all the files in the Blockset folder in the castle_tower folder that contain the word "roof" in them, but they still keep appearing in my game.

How can I remove the roofs from the tops of my fortresses' towers? Or rather, how can I substitute a different model for Northern European fortress towers?

Thanks!