Hagrid was sitting at his table, where there were two large mugs of tea. He looked a real mess. His face was blotchy, his eyes swollen, and he had gone to the other extreme where his hair was concerned; far from trying to make it behave, it now looked like a wig of tangled wire.
I'm not sure if I understand that part correctly. In my opinion, the word 'concern' here means 'worry'. So, it can be rephrased as: he had gone to the other extreme at which his hair was worried.
But I really don't know if I get it correctly?