Did he tag you defensively or do you think it's feeding response? I've never had one change temperament on me. In my experience they're either snappy or not lol. Next time I would just try to touch his body from behind so he is aware of you and doesn't pick up on the temp of your hand. I find that if they are looking to eat this will generally snap them out of the feeding mode. Then just be as gentle as possible while picking him up and handling him. The more gentle and calm you are the better the reaction from the animal in my experience. I've always heard of conditioning them but I've never really tried it. Hopefully that will help, best of luck.
Also Bogertophis brings up a good point about possibly going into shed or something stressing him that you're unaware of.