That sounds like a good starting point, with modifications for specific circumstances and with the caveat that if you lose the prereq due to abilities of the prestige class itself (e.g. half-dragon), you don't lose abilities because of that.Krelios said:For what it's worth, I use a houserule that all Supernatural (Su) and Spell-like (Sp) abilities granted by a PrC are lost if the prerequisites are lost, but any Extraordinary (Ex) or "mundane" abilities (including BAB, HP, Skills, Saves, Spellcasting [if it's +1 to existing], and even bonus feats, etc.) are kept. In no case can a character take a level of a PrC (first or otherwise) if he does not meet the prerequisites when it's time to level up.