You can sort of do this through modding, but not in-game. Paul has said that he is concerned that allowing players to design fighters would be really hard to balance.
As I put in another thread.
Keep the components list fixed, but let people pick the hull look. That way they can keep fighters in their races theme while not damaging balance, it's a nice compromise.
Alternatively the fighters could be 'components' of the main carrier ship, or just have a box linked to it, that you click to customize.