Yes, you can definitely over feed any animal. However, most breeds of chickens are pretty good at. deciding how much food they nee on their own. If you are feeding a high. quality commerial diet, free choice is usually ok. For meat breeds and cornish crosses, you may need to regulate their feed more to prevent overgrowth and leg problems. If you flock begins to gain too much weight, you can cut back the amount of feed available.
What is worse than overfeeding is feeding a diet that is not balance and lacks the proper nutrition for healthy chickens. I see this occur often when people feed home made diets.
Your birds need a good balanced diet available free choice, which means that the feeders never run out of food. My feeders are filled all the time, so from dawn to dark, everyone can eat all they want. Cornishx birds are a special (very sad) case, not confused with normal chicken rearing. Mary