I feed all my snakes in their cages and have never had a problem when I want to take them out. As long as you don't smell like a rat when you open the cage there should be no problem. I water my snakes every 2 days and have to open the cages and they have never struck at me when I do that. Most of the time they are sleeping anyways.
As far as mean boas, my 8 ft. rescue RTB was mean when I first got her, she would always strike at the cage when anyone got close. I think proper care and treatment calmed her down tremendously. Now I can take her out without worrying about being bitten.