Drop your mod into the mods folder here: C:\Program Files\Stardock\Galciv2Ultimate\Twilight\mods
Then:
1.- Start GC2U
2.- Select the options button found in the Main opening screen menu.
3.- Once into the Game tab options (second column on that screen, first group of items, top of that section). Click CHANGE.
4.- Click to USE any of the installed mods. Click DONE. Not default, not cancel, DONE.
5.- Click the USE MODS box.
6.- Exit GC2U.
7.- Re-start... your mod is active.