This file has less of an impact during character creation than some would like, as the game is hardcoded to allow (at most) only the first eleven rows (the standard base classes) as choices for a new character. (The Player Resource Consortium circumvented this restriction by developing a character creator that is external to the game.)
So I have to get PRC to be able to take the illegal char I made up?
You can hijack one of the base classes - for example, I replaced Barbarian with a custom class in one of my modules - but of course that renders the module unplayable with existing characters of that base class.