The glass needles reroll the 3-stat spread (Intellect, Discipline, Strength) and the extra special abilities. Do note that certain exotic armors have different spreads, so it may limit the random chances for changing things, like one armor may only allow Dis and Str, so you'll never get Int on it at all. Do note that RNG is still RNG. There's a chance after rerolling that you'll end up with the same thing (or close enough that you don't notice any different from looking at it). Some armors have higher chance than others because of the limitations as mentioned above. Usually the changes noticed in such situations are the extra abilities, because the stat adjustments tend to be so close. The XP put into the piece of equipment to gain access to the nodes and materials used to unlock them are not lost. If you've already fully upgraded a piece of armor and then use a glass needle on it, it may change the nodes, but they won't suddenly lose all progress. This is normal. Rerolling the old way back in TTK and the old Iron Banner weapons did such (reset progress on the equipment), but the glass needles don't.