Yes and no.
Skins have never been canon unless they are specifically connected to the lore in some way. AU skins definitely aren't. Galaxy Slayer Zed, for example, is from who-knows-where in space, and he has a damn symbiote from the looks of it. Normal Zed would not look like that.
But even then, holy shit that is such a huge deviation from what we all think Zed looks like. Its very jarring and weird to look at, especially when you have pre-established expectations as to what a character looks like. I'm not sure if I trust Riot now after this.
So, yeah. Even though skins are meant to change the character in some way, Jhin has stayed overall the same in all of his skins. Jhin has always been a mystery. Nothing about him his real, not even his name. Everything is an act, a fabrication. The mask is a constant. They didn't even have to give Jhin a mask in PROJECT, since he doesn't really have a face to cover anymore, but they did anyway. Same thing for High Noon, as both are robots with no true faces. Its clearly a very important part of his character, and something that should not be taken away.