How the fighters are chosen is set in the XML, so you have no control over them and the games blueprint system handles what they come equipped with. 

They get the best tech available.  So if you unlock the next beam weapon tech the next time your carriers go into battle their fighters will be using that weapon.  It's basically a way to cheat the upgrade system and keep your fleets competitive without a penalty in turns to upgrade or cost of upgrades.  Personally, I think it's a bad system.