You're close but in the wrong area.
Code:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"HideFileExt"=dword:00000000
"Hidden"=dword:00000001
show and hide files is a profile specific key and therefore can be modified by user accounts. if you would like to change the default, navigate to key:
HKLM\software\microsoft\windows\current version\explorer\advanced\folder\hidden and \hidefileext
there are keys in there that set default behaviors.