Can't change prohibited school

[Fionn]

Did you take your first level of wizard on a level other than first level? IE did you start as another class first? I've heard of it bugging like this when the wizard level is taken later on in the character's progression.

I'm in the same boat, Swash 5, then Wiz (Abjurer) 5 - I found the feat to select an opposition school (Necro), but it still says I'm a generalist with an opposition to Necromancy. English game from GOG if it matters.