Windows 8 UX Pack will give you Windows 8 UI improvements such as theme and logon screen without touching system files at all so it won't have such risk to harm your system at all.

In this package, you'll have Windows 8 inspired themes and applications to make your system resembles Windows 8 as much as possible without modifying system files. Give your desktop a visual boost with the Windows 8 UX Pack.

Features:

M3 user interface for installation/configuration

One-click installation/configuration

UxStyle memory patching

Windows 8 Aero Glass or Lite theme

Instant M2 and M3 wallpaper/logon screen customization

UserTile with current user/wallpaper auto configured on login