Gae Dearg doesn't cut through stuff whether it's permanent or not. What it cuts is the flow of magically energy. If you would see an armor enhanced to be harder than that armor would have been Reinforced. That's permanent, but Dearg can cut through stuff like that. What the energy is doing in that case is making the armor harder, when Gae Dearg touches that the energy is cut and the armor is no longer magically hard. How i know this to be the case? KoO. What KoO does is reinforce objects to be on the level of NPs, but Dearg can cut through those as easily as anything else