I am thinking of changes which could be made for realism for a mod. Infantry can shooting from greater distances (with line of sight), but are more likely to hit each other from closer ranges or garrisoned positions. When they do hit, they cause greater damage. With higher experience, they have better accuracy. Are these kinds of changes even possible with the engine used by Generals?

You're better off using projectiles rather than the instant hit/hitscan weapons.

You can make the bullet be an actual projectile, like in tanks but travel faster or something. With a projectile, you can have the property of it hitting things that you don't mean to target.
Along with using a projectile you can use ScatterRadius and ScatterRadiusVersusInfantry. Which basically is "the projectile will land anywhere from the radius of indicated.
Just be sure your units have a WeaponLaunchBone.

I do not recommend setting this value beyond 20 because that means the weapon will be horribly in accurate unless you it's an intended joke or if you're dealing with Multi-rocket launching system.

As for being more accurate, you can nake veteran, elite and, heroic versions of the said weapon, reducing ScatterRadius/ScatterRadiusVersusInfantry. Just make sure you implement three weaponsets having "VETERAN," "ELITE" and, "HEROIC" as the Condition on them.

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