A minor update was just added - a line had been dropped about not being able to unlearn a class that can only start as (such as Wild Mage). This has been added back in.
Lord Gideon Weaveforger of Kaladonia
Steward of Elvalion OOG: Geoffrey Schaller
Let's say, for example, a character has only one profession list that appears on his race's starting professions, and three that didn't. Could he unlearn the profession from his starting list?
That is something that did not come up but I would venture to say no. One of the spirits of this system is that a character must be concidered valid after the retraining happens. By removing your only list which is concidered a starting list your character is no longer 100% legal via the current rules surrounding character creation and progression.
Lord Erdrick Brightstar
Guardian of Belladeen
(Samuel Roberts)
No, because the rule stipulates that your character card must be legal when you're finished. Having three professions that you could not have started with and none that you could have started with would make for an illegal card.