They don't "really" need to change the code as much as they need to randomly mix it up a bit. In fact, they could write a program to produce the New Age Changes for each coming age!
But there isn't really a point to delaying the age to "fix bugs" if bugs aren't going to get fixed by delaying the age!
The new age changes don't really change anything, the only "new bugs" are just small, minor, glitches... nothing really core based.