Rockstar has released an official statement saying that while the EULA on banning the use of mods will not change, they will not be banning anybody who uses mods in single player. The reason the EULA states anybody using mods will be banned is that by definition, mods are unauthorized, but Rockstar is fine with mods as long as they are not in multiplayer.
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which is why they totally banned people who were using single-player only mods like sweetfx or FOVslider