Some environment events cause a site/region type to be treated as other site/region type. Using a word treated instead "changed" (or "becomes") is not accidental. This indicates that no change is applied to an object, rather an object is under an effect. Once the effect disappears (sometimes along with a card that cause it), the object is no longer treated in some way.Witch-king of Angmar wrote:Unique. Nazgûl (1st). May be played as a hazard creature (with one strike) or as a permanent event. As a creature, may also be played keyed to Angmar, Gundabad, Gorgoroth, and Imlad Morgul; and may also be played at sites in these regions. If played as a permanent-event, it will remain in play until tapped during the opponent's movement/hazard phase (tapping counts against the hazard limit). When tapped, Witch-king of Angmar becomes a long-event and causes all Shadow-holds to become Dark-holds .
To make the Witch-king of Angmar's effect to be working in the manner I propose the following erratum:
Unique. Nazgûl (1st). May be played as a hazard creature (with one strike) or as a permanent event. As a creature, may also be played keyed to Angmar, Gundabad, Gorgoroth, and Imlad Morgul; and may also be played at sites in these regions. If played as a permanent-event, it will remain in play until tapped during the opponent's movement/hazard phase (tapping counts against the hazard limit). When tapped, Witch-king of Angmar becomes a long-event and all Shadow-holds are treated as Dark-holds .