I have never done that and never had problems ..... It's been my experience that the snakes react more to the smell of prey, rather than the action of opening the cage before feeding..... If I even walk in the snake room with a rat...all of the snakes get excited and are in feeding mode....and if I would reach in any of their cages then I would be lucky not to get bitten.
I don't have any problems reeaching in the cage when there is no food scent in.
I think that snakes probably don't have the cognitive ability to associate things like that....but I'm sure you will find alot of differing opinions.
If you have one or two snakes then maybe feeding in a separate cage would be an option.  But  multiple snakes make that a little unfeasable.  I personally don't think it is necessary.  Keep him in his cage....it's a secure place for him, and snakes feel even more vulnerable and stressed during feeding sessions

Not so much a black and white issue here, there are many exceptions to the rules. I work in a pet shop, Animal Trax, and I'm in charge of feeding the snakes. We feed nearly every snake outside of their enclosure. Having multiple snakes in one tank does make it impossible to feed in the habitat(I have heard horror stories!), but that is only one reason. Most of our snake are eating FT and the possiblility of them dragging bedding and other depris in with their meal is something we prefer to avoid. My son currently owns a ball python we nearly put down because of a large blockage from ingesting some bedding(it was a hatchling that came to us in that condition). I worked with the snake for over a week to get it back on track, she had eating issues for a while, but is thriving now. Like I said, there are exceptions, we do have a few snakes who will not eat unless they are fed live prey in their enclosure. These are watched closely and defecation noted. We've made efforts to change this, but without success. With my personal collection, I feed all my Chondros in their tank from their perches(a given!), but I also have a BRB who will only eat in his enclosure. All others are fed in seperate containers. The size of the container makes a difference, too. The smaller the better. Too large a container and they explore the space before concentrating on eating. As for those really large snakes, we don't keep those in the shop and I'm not familiar with their feeding habits. Other on here are better equiped to answer. The "cage aggressive" animal is, in my opinion, that way for reasons other than just feeding in the tank. I do feel like some snakes can become "conditioned" to certain behaviors on our part and react accordingly. Most of the time, husbandry, or lack of, and carelessness play a large part in whether or not you get bit!

Occasionally I'll feed outside the cage- and thats usually when I have an 'audience', or its picture time, or because my one sibling girl is a doofus and sometimes won't eat unless I stick her and the food in a paper bag.  I really haven't noticed a difference whether I feed in or out- minus the one girl, my carpets all love to eat. I've tried seeing whether or not if I stick my hand in there and just keep it there if they'll try to go for me as food-- and they don't. They all come up slowly and investigate, then either leave or crawl on me. I stick the rat in.. come up, investigate a lot more quickly, and BOOM. Struck and coiled before I can blink.

Do you think maybe he's associated his old cage with eating? What if you moved him in there just for feeding? Or maybe an hour or two before feeding so he can relax a bit, then feed and when he's done move him back to the new cage?   2/5 of my carpets have been very timid- including when with food.