The vast majority of changes have to be made by altering the hex code of the game executable file XComGame.exe, either directly or indirectly. Despite the presence of various configuration files, for the most part the ones you would expect to be able to 'tweak' to have an effect are not actively used by the game itself by default, except in a very limited set of instances. XCOM:EU 2012 is not (at this time: April 2013) considered a 'modder friendly' environment. 'Long War' is not compatible with other mods that are not specifically written for use with it, even if they work with the vanilla version of the game. The popular 'Long War' (LW) mod is not an official release from Firaxis, but is so extensive a reworking of the game it is regarded by many as another (unofficial) expansion. EW mods can not be expected to work with EU, and vice versa. Mods are written for specific releases, and are not generally interchangeable. The later expansion release (as a 'DownLoadable Content' or 'DLC' addon) is known as 'Enemy Within' (EW). Note that the initial release is called 'Enemy Unknown' (EU). Use the Steam 'verify local files' option in the Library section of the Steam Console and it should replace the affected file. If you believe you have a legitimate Steam version of the game, then this is indicating a corrupted file.

(Even the version sold on CD requires a Steam account and internet connection.) The Nexus site rules prohibit anything supporting piracy or help with this problem.

If you are getting 'application error 0xc0000142', you have a so-called 'non Steam' (as in 'cracked') version of the game. First of all, it is not possible to modify XCOM:Enemy Unknown 2012 (XCOM:EU 2012) for any game console.

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