It is possible to add mods to a saved game: you can enable mods and load a saved game made before those mods were enabled. If you plan to enable multiple mods at once, we recommend checking the mods' documentation for information about their compatibility with other mods. Enabling incompatible mods may cause the game to crash. Many mods are incompatible with each other. The vast majority of mods are made by amateur developers: many mods have not been thoroughly tested, and some may cause crashes or other stability issues.

You'll find full instructions on using mods below. To access the Mod Manager, select the Mod Manager tab on the pre-game Options window (this is the window that appears when you launch the game). Once you have installed a mod, you can enable it by using the Mod Manager. There are two ways to install mods: you can either subscribe to mods via the Steam Workshop (this installs the mods automatically), or you can download mods from other sources and install them manually.

Xcom long war mod manager