Question: Is The Ninetales evolved from Tanya another mask, or is this another suit or somethin else entirely?
I wanna know: Did her suit evolve or somethin?

I think it her future from and she got the power to take anyone face where the victim TF into a mannequin and replace it with a another mask on her tails or modify the mask to someone else

Oh. Manipulation of faces, kinda like the Spirit World lore in Avatar: The Last Airbender. Nice. :3

Though, now I do wonder... Kitsunes are said to wear masks using a kitsune mask that looks pretty much exactly like them, as if they were a fox also. ;3
Wouldn't that mean that these fox masks can transform her as well, or am I thinking bout it way too into it?

Kinda like Majora's Mask, the inspiration of masks were transformative masks possessed by spirits that haunt someone until they take it off.
In various folklores, those masks irl are actually cursed, whereas Majora's Masks creates an addition of being able to take 1 off.

1 story recounts a tale of man who found a strange fox mask. He tried it on, & couldn't take it off no matter how he tried! Then he became a kitsune, fully transformed into a fox or youkai, on interpretations as well. The story recounts to not pick up strange masks you may actually end up meeting! Particularly worded because of "meeting a friendly face", recounting to be careful when picking up anything face-shaped as well.

More stories recount times foxes used masks to escape prey, predators & hunters altogether as well, based on various fox youkai lore like the kitsune have!
This is only 1 aspect of it, since foxes ALSO use masks to disguise themselves at a festival as a regular party-goer as well. ;3

I guess what I'm asking is, can her masks tf someone or only her only? Like, exclusive to her, or no?

Yep and tbh, still WIP for her

Ah, still figuring out who can use them. OK, I'll let you figure that out, then. ;3

Yeah ^^