Per my understanding, once Arya Stark killed the Waif in Game of Thrones S06E08 ("No One") she came to Jaqen H'ghar and finally admits that,
A girl is Arya Stark of Winterfell. And I'm going home.
So she seems to renounce any ties with the Faceless Men and to have found her real self back again, after a time of confusion about herself and her legacy, to Jaqen's apparent satisfaction.
Then in S06E10 ("The Winds of Winter"), how is she able to still use the faces
when killing Walder Frey?
I thought this magic is only reserved to the Faceless Men who truly became No One. Arya, though, is someone and is done with the Many-Faced God, yet she still can use the faces at her apparent disposal (without even being near the "face storage" in Braavos). Why/how?
This might be based on a lack of understanding from my side about how this "face magic" actually works. Is it just an accquired skill that you can then use however you want (maybe only requiring some "willing" corpse to provide its face)? Or is it tied to other requirements that Arya already fulfills, albeit not belonging to the Many-Faced God anymore? Or does she maybe even still belong to the Faceless Men somehow? Or is she using the faces "illegaly" as she did before?