It hardly matters in any case, as the "code" doesn't open the door. The "code" sends a request through to the pilots, who then check the area, and the reason for the code being entered, before they decide whether or not to open the door.
The "code" is only of any other use if both pilots are incapacitated - in which case you have more to worry about than who knows the code. If fact in that case, regularly changing the code would have an adverse safety impact - the people who need to know it may not remember the last change!