Not that it's relevant to the OP's topic and thread, but I suppose a hack-job way of doing it Stabbey, could be to check all abilities values and if they're =>+1 their default value, subtract that value by the default value of the ability type and remove those points and then add equal points to thievery/scoundrel after game start.

It's a hack-job because players would still be led on to believe they can choose in character creation, but is overridden after the game begins.