darkgalaxy30
By adding a new part in a mod file. 😄
If you don't know anything about programming you probably won't understand anything of it, but mod.txt files can basically tell what they do if you understand the coding language. There are examples enough, just be sure to use mods that are compatible with the most recent game versions.
I also suggest taking a look at some modding guides on the forum. (https://forum.cosmoteer.net/d/6811-introduction-to-modding)
If you have a question, just ask. Perhaps I or someone else is able to help.