"You have a bonus to attack and damage rolls."
Thus, its not "extra" damage, it's an increase in the weapon's normal damage roll. Which, for a mace, is bludgeoning. For sneak attack, it is "extra damage", but it says "The extra damage’s type is the same as the weapon’s type". Which for a mace would be bludgeoning. Ergo, if a spell or ability changes the normal damage of a weapon, then any +X damage is also changed, because it is part of the normal damage, and sneak attack is changed because it always does the same damage as the weapon's type, which has been changed by the spell/ability.
Now, consider the dragontooth dagger. If I sneak attack with it, the sneak attack damage is piecing, not acid, because "piercing" is the damage the weapon does because of it's type. It's the dagger's normal damage. The +1 is also piercing, because this is added to the weapon's normal damage roll.
Unlike sneak attack, the extra damage is specified as being acid, not "the same as the weapon's type". Thus, an effect that changes the weapon's normal damage type doe not affect this extra damage, because it is specified as being acid damage, not normal damage.
Note that if the intent was to affect all damage done by the weapon, then there would be no need to include the word "normal" in the text. It would be redundant.