Access Windows registry from limited account

i'm trying to prevent users form changing the wallpapers on the computers they use. so i do it through the registry using this tut...http://www.askvg.com/how-to-prevent-users-from-changing-desktop-wallpaper-in-windows/...

The thing is that upon accessing the registry in the limited account i cannot change nor edit anything is their a way around this.. i also tried to set the permissions for the account but upon using it.. the access is denied...

You should be able to do this from your administrator account for all limited users, without having to log into those accounts directly