I have only been keeping clowns for about 2 years. I always make it a point to hand feed my clowns. Easiest with a good flake. Mine never have bitten me or shown any kind of aggression toward my hand. I have a large GSM about 5-6" and her little hubby in a tank along with a clarkii and an ocellaris, had a system malfunction so they have had to share my 92 for a few months. I also have a pair of black ocellaris in my little 29.
But across a variety of clowns it seems they recognize me as the food master and so they don't bite the hand that feeds, at least not yet.