How Mods work
The engine will attempt to find the files it needs in mods before searching the root game path. Mods work by simply providing the different files to use.
Mods (short for modifications) are a variety of fan-produced content that alters the game. Numerous mods are available for Sins of a Solar Empire: Rebellion. Sins supports mods internally, and the developers have went to great lengths to support modding, even incorporating numerous bug fixes made by the community into the 1.2 patch for Trinity/Diplomacy.
A common category of mods are total conversion mods, which use the framework of Sins of a Solar Empire to depict a conflict set in a different franchise.
See the Setting-up Mods page for more details.
Partial List of Mods
Among sources of additional mods are the Sins forums