An opponent controls a planeswalkers with Luxior, Giada's Gift attached. If I turn Volrath, the Shapestealer into that creature, can I activate the loyalty abilities of that "Planeswalker"?
A loyalty ability of a permanent can be activated even if that permanent isn't a planeswalker. But even so, in general, only one loyalty ability of a permanent can be activated in a turn, and only once that turn (C.R. 606.3). Note that the cost to activate a "-N" loyalty ability is to remove N loyalty counters from the permanent where it appears (C.R. 606.4, 107.7); this is true whether that permanent is a planeswalker or not.
Also note, that Volrath becomes a planeswalker but doesn't have any loyalty counters nor does he get any from the copy process. Thus Volrath goes to the graveyard before you can activate any abilities for being a planeswalker with 0 loyalty counters.
See also:
Former Rules Advisor
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