I'd wait to worry about this until after he's sound again. Abscesses are horrifically painful, and do you feel at your best temper when you're in pain? He's most likely defending himself before it's needed because he's in pain and not real quick on his feet. Like Borderbratz mentioned, injured or weak horses are often shuffled to the outside of the herd if they are too passive, and instinctively, this usually meant death by a prey animal.

My old gelding suffered a painful injury several years ago, and he was much more aggressive and harder to work with due to pain and confinement. He returned to his normal personality as he healed and received more exercise.

I'm willing to bet that once he's sound, back to turnout, and feeling better, you will have your old horse back. Give it a few weeks and see how it goes.