There are rules for a Cleric who loses faith, and how to regain his standing through atonement.
But what if he abandons one faith entirely for another? Presumably his new god/faith should be picking up where the other leaves off, so spells aren’t interrupted, and further he probably should be changing his Domains to ones used by his new faith, but does any official book actually describe this process? Does his new faith require atonement for his prior faith in another religion? Is there some kind of interruption time period, where he doesn’t get spells? Is the actual process of substituting Domains explained?
Because the lack of rules that I’m looking at almost seems to imply that a Cleric cannot change faiths.
I’m really looking for book citations here, because this is specifically for the sake of determining what the rules currently are to better judge how changes might affect them. I have plenty of my own ideas about how this sort of thing should be handled, most of which rely on eliminating as much of alignment’s mechanical impact as possible, but that’s not really relevant here.
If your answer is that there are no such rules, I’d like an idea of how certain you are of this. For example, I could not find any such rules in Player’s Handbook or Complete Divine, the first two places I looked. Knowing where the rules aren’t is useful.