There's no such thing as "turning it off". There's nothing under the skin - there's a pre-defined set of skins and you just choose which of them you want.

In my case, I don't want the default skin - I want my users to see a simpler interface. So I set this regtweak at T-12:

[HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer\Player\Skins]
"CurrentSkin"="res://wmploc/RT_TEXT/corporate.wsz"

You don't need to copy or put that skin anywhere - it comes natively with WMP8 (or higher).

Please try that and tell me if that was what you wanted too.

I'm using this now:

[HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer\Player\Skins]
"CurrentSkin"="res://wmploc/RT_TEXT/corporate.wsz"
"LastViewModeVTen"=dword:00000001

And this is exactly what I wanted.

Thank you.