Originally Posted by
mattie_p
A 165: No. Lacking rules text on Ex-Ur-Priests (see Ex-Bards, Barbarians, Monks, Druids, Paladins for examples), and defaulting to the DMG rule on Prestige classes (must meet criteria for first level only) an Ur-Priest does not need to remain evil.
A 166: Correct. Without an Ex-X section, other notes on the topic, and outside of Complete Warrior/Arcane. Otherwise, an Ur-Priest would be useless, as it grants the ability to cast divine spells while requiring the character to forever forsake previous divine casting ability.