find an English noun that means "something that has to be changed."

How far shall we extend the definition of change?

If we change a diaper we end up with a whole new diaper albeit equivalent to the old, just cleaner. If we change a baby we best come out of the process with the same baby as we went in with or momma ain' gonna be happy. If we change a line of code we better have something that works differently than the old.