The Morphling |
Pathfinder Adventure Path, Lost Omens Subscriber
As far as I can tell, Slashing Grace does not in any way alter the damage dealt by the weapon it modifies. Flavor text is not rules text, so "you can stab people with a sword" is not applicable here.
It says you can treat the weapon as a piercing weapon for the purposes of class features which require one but never says it deals piercing damage now.