Modders have never really needed a developer or publisher's blessing to do their work, but EA and Maxis have, nine months post-release, begun to allow official mods for SimCity. There are some caveats to being an official mod however: according to a post on the SimCity blog, you can't modify any executable files (.exe, .dll, .so, etc), can't use copyrighted material, can't use material unbefitting of an E10+ rating, and cannot "jeopardize the integrity of the gameplay" or "affect the simulation for multiplayer games and multiplayer features."

While the first three items on the above list could be described as "restrictive," it's the rules about "jeopardizing the integrity of the gameplay" that raise eyebrows. In March, Maxis General Manager Lucy Bradshaw tweeted that "the game was designed for [multiplayer]," and reiterated in a blog post that a single-player mode "didn't fit with our vision." So if the game was designed with multiplayer as an integral gameplay experience but mods can't affect the multiplayer simulation or "jeopardize" gameplay, this may be the most restrictive clause of all.

EA also has the right to use, copy, modify and/or distribute an official mod without asking the creator's approval, without paying the creator, and without crediting the creator. So feel free to change the game, modders; just don't change it too much, and don't expect to get paid or credited.