Allow Users to Set Any Screensaver Except None

GPO

User Configuration -> Preferences -> Windows Settings -> Registry

New Registry Item

Action: Update

Hive: HKCU
Key path: Control\Desktop
Value Name: SCRNSAVE.EXE
Value Type: REG_SZ
Value Data: C:\Windows\system32\scrnsave.scr

Common Tab -> Item-Level targeting

the registry value HKCU\Control Panel\Desktop\SCRNSAVE.EXE does not exist
 

Reference

http://www.grouppolicy.biz/tag/screensaver/