Currently, there is no way to reproduce advanced guided missiles behaviour by script or cfg.
The only thing you can actually do is to make your vehicle fire a selected missile at the desired target (fireAtTarget).
If the missile can't see the target, though, it just flies straight.
The cfg values are restricted to

Take a look a the AGM-88 for example, it has three fire-modes :
Opportunist mode : the missile flies straight ahead, gains altitude and searches for potential targets. Once found, the missile stops gaining altitude if it did and flies towards the target.
Classic mode : the missile is fired in the supposed direction of the enemy, and locks it's target after launch.
Defensive mode : the missile is fired on a locked target (implemented in ArmA) keeping the same altitude while the target is not just below it (to score a top-armor hit, and that is not implemented in ArmA).

My request :

• Implement a new cfgWeapons value (smth like guidanceScr = "myFile.sqf";). It would define a script launch if this guided weapon is fired. Useful arguments could be the projectile itself, it's target (if already locked through Tab or Right click) and eventually the fire-mode used.
• Implement some script projectile interactions. Like _missile lockNewTarget _target;. It would be great if the missiles or bombs could lock on coordinates, too.
• Implement a new CfgAmmo value (like dispersion = 1.5; // meters) to simulate targeting errors. A laser-guided missile doesn't always score a hit exactly where the laser is.
• Implement a new CfgAmmo value (like detonation = 5; // meters) to simulate proximity detonation of AA/AG missiles or bombs (to increase the hit surface)
• And other basic things, Javelin-like top flight pattern, auto-climb to avoid obstacles, more interesting counter-measures usage, ETC...