The implementation of this is something I have no clue of. I don't know if the user id has any permanent identifier that does not change with the username. I think one way to combat this is with the mobile app but the following should apply for the steam game. So let's say by linking your twitch to the MOS app you are creating an app-specific account which you link your twitch to. Or you create a separate account with email and pass and then link your twitch. Either way your twitch is now linked to an account that permanently carries your stats for the season and despite the name change your stats will stay. Again, I don't know if this is even how it would work/be implemented but we all may change our name for one reason or another and are devastated by losing these stats we worked hard for.