Re: A Weapon that creates wounds that can only be healed by a particular method.
First, let me say I've never even seen a 6th Ed book, so I'm speaking from the 5th Ed perspective: Since it is a property of the weapon, and not the Regen's inability, I fall on the side of it being an addition to the weapon itself, not the Regen (unless it's because the weapon is made of a certain substance - like silver, cold iron, some rare mineral, etc.).
That being said, Transform seems a bit clunky and like we're trying to fit a square peg into a round hole. Why not just create a campaign-specific Advantage to add the weapon (value dependent on the prevalence of Regen and how difficult it is to get it healed) that states, "Damage Cannot be Healed by Regeneration" or a statement of what exact method must be used to heal it? I'd say look at "Cannot Be Dispelled" as an example.
Just my two cents.