On an aside, computer use can cause eye fatigue, but doesn't cause any permanent effects.

Back on topic, I'm letting the comparable type character in my campaign increase his powers just like a fighter could increase his natural strength. If your main concern is that it's unbalancing to give him additional powers though then that should be reason enough to disallow it. You could attach a side effect to his changing outside of a humanoid form. Maybe he takes damage from turning into such odd forms or maybe it costs endurance because of the strain.