Pokémon Let’s GO: Changing Mew Nature using PKHEX

[Mugenblst]

Hi, this is my first time playing a Pokémon game(I’m a N00b). I have a question regarding Mew in LGPE and PKHEX.

I got a Mew from a Pokeball plus that I bought. Is it possible to:

1) Trade it to a friend that has PKHEX and have him change the nature of the Mew using PKHEX and return it to me.

And after that is done, would it be possible to:

2) Use that Mew online without any repercussions? Does Nintendo keep track of the Nature of the Mew when it is redeemed or do they have no way to tell that the Nature was changed?