Hmmm, Mr Piggy's cage aggression was so bad when I got him that I couldn't even put my hand inside his cage without him going after me, let alone try to touch anything. I normally do the cage cleaning and changing /cleaning of the food and water dishes while he is out on his playstand. He watches me with a keen eye, probably to make sure I'm not eating his food? I have not tried touching his food dishes when he is IN the cage, I believe I'd like to keep my fingers attached to my hands just a little while longer.
We will work on this eventually as well, right now I am happy that he will step up onto my hand from any perch inside his cage, even the one all the way in the back without trying to take chunks out of my finger.