Step by step? No. It's all in text, and it wouldn't be worth the time to post a step by step guide, in detail, to making a full working mod.
Just go to c:\program files\stardock\totalgaming\galciv2\data\english.
Modding the XML files here (races, techs, weapons etc) will modify them in game. If you changed the name of the Dark Yor to the RIAA, and gave them a backstory of having the custom of obliterating creativity and suuing minors...
Then in game you would meet the RIAA, an evil race with a custom of obliterating creativity and sueing minors.
It's just notepad editing, nothing more.