Yes, it is possible, a colleague of mine replaced the battery of a 2012 MB Pro. It is possible, but not easy and involved chemicals which should not be handled by anyone without basic lab experience. Things have become somewhat better but still the question is: why isn't it easy and why doesn't Apple offer battery exchange for a longer time? If they really care about the environment, they should at least offer to fix your old MB at a reasonable price. (At their typical battery replacement prices, there should be a healthy margin anyway).