По пути HKEY_CURRENT_USER\Control Panel\Desktop добавлять через reg add параметры, например:
"ScreenSaveActive"="1"
"ScreenSaverIsSecure"="1"
"ScreenSaveTimeOut"="300"
"SCRNSAVE.EXE"="C:\\WINDOWS\\system32\\%name%.scr
Код:
reg add "HKCU\Control Panel\Desktop" /v "SCRNSAVE.EXE" /t REG_SZ /d "%windir%\system32\scrnsave.scr" /f
