Security – How can I reset my Apple user permission

so this MBP currently has two Admin users and the user. For the user account specifically, I added Chrome policies of which I do not want anyone, except me the administrator, to access the plist. So the list is in "/ Library / Preferences /". Every time I select "get information", I open the sharing tab and permissions no one Easily has the ability to change the permissions to "read and write" without having to enter admin / pw. Here is the warning, it only happens in that specific folder, since in a program where I enabled "not to have access" to all, but the administrator prints "You do not have permission to open the application"

Some things I have done:
checkoff & # 39; d / security & privacy / general / advance / require admin for the whole system
"diskutil resetUserPermissions / $ (id -u)" <-minus parentheses

What am I doing wrong? Why is it that someone has the ability to modify the file without requiring admin / pw simply with the permission to "read and write"?