How to change system preferences programatically, 10.5 issue

Question

I know about the "preferences" api. Like SCPreferencesCreate(NULL, CFSTR("SomeName"), NULL);
and get value and all the rest.
In fact, I know how to read all the preferences.
The problem is changing them. I do not care which one, any of them. You see, these are on "const" or non-mutable. So you are going through a dictionary and want to add a value. So you use CFDictionaryAddValue(..).
On 10.4, this is fine. On 10.5 is crashes with an error (the newer XCode is much nicer) saying I am trying to add a mutable value to a non-mutable collection. So any CFDictionary is non-mutable. I can create a mutable copy, and do whatever I want, but I can't save the changes into the original preferences file because its non-mutable. Now I can of course create a non-mutable value, like a CFArray or whatever, but the CFDictionaryAddValue(..) only takes Mutable items.
This seems to be a catch-22 situation.

Answer 1

The problem was this. You would Start with PrefGetValue getting "A", but needing to change "C"
A
--B
----C
So you can get and set A, but it is C that needs to be altered.
I figured it out and it was a solution I kind of suspected, but didn't want to deal with, because what if you wanted something really deep like H or Z or whatever.
What you do is Get A, make a mutable copy of A. Then get B (from mutable A) and make a mutable copy of that, and repeat until you were at the thing you wanted to change. Then you change it, then rebuild the dictionary structure in reverse. SetValue C, then Set mutable B's value to Mutable C's value, then set Mutable A's value to Mutable B's value, and finally use SetPref using Mutable A instead of the original A.
Apparently 10.4 didn't consider the prefs non-mutable so everything had worked, and under 10.5, they are non-mutable and you crash if you try and change it.