bvtech,
That isn't something you should change easily. Those are loaded from the get go via the software installation and during an upgrade they will most likely be replaced; depending on the upgrade that is.
We have had customers do custom prompts, but it never lasts long.
Unfortunately I do not remember what all of the prompts are that would have to be recorded. You will need to call Mitel and ask them about it; I am sure they have it documented somewhere.
Thanks,
TE