This is not a problem, you can very well make a plugin that will affect the accuracy of the gun for everyone and not just a bot.
Make your plugin hook the TraceLine function. Then, do a check on pentToSkip to know if it's a player (having the FL_CLIENT flag set), and if so, to know which gun model he's carrying (check for pentToSkip->v.weaponmodel). Once you know it's a player with a Mac10 in hand, just modify the return results of the TraceLine yourself the way we described and make the function exit with your modified TraceResult
