The FAQ states: "From a setting standpoint, such a career transition is highly unusual.
Leaving an established Empire Cult or the Colleges of Magic
would meet with suspicion, questions, and possibly persecution.
A wizard leaving the sanctioned and approved Colleges of Magic
could well be branded a hedge wizard, sorceror, or dangerous renegade
and find himself targetted by zealous Witch Hunters."
But this presupposes that the wizard 'leaves' his college. i.e. Send a letter of resignation or simply denies membership if asked. This is indeed ridiculous in the setting. However, a more organic scenario can be imagined:
A Bright Order wizard apprentice is instructed to spend a year adventuring before he can be initiated as an Acolyte. Six months later he finishes his apprentice career and decides to improve his melee skills. He asks his Dwarf Soldier friend for combat training. Never one for half measures the Dwarf sets the lad a punishing training schedule – treating him like any new recruit.
For the next six months the character invests his time perfecting martial skills and talents and exercising to improve his strength and toughness. While in the Soldier career he still wears his robes, symbols of college membership, casts spells and obeys college orders. He may or may not have time to complete this career before reporting back to his college. How is his college even going to know he has changed career? His masters might notice that he has spent time training his martial skills, but is this really so nonsensical for a future battle wizard?
I looks to me that the FAQ entry is overly proscriptive.