Windows File Protection
The file sfc_os.dll is responsible for the Windows File Protection. When you try to replace a protected file/folder, you'll see one of these prompts:

If you really meant to replace the file, then a simply press of Cancel solves the problem. What if you didn't want to take the time to press Cancel or the protected file is already in the DLLCACHE folder, then read on to disable WFP.
If you're one of those people that want a prepatched version, scroll to the bottom of the page for your files.
» Hacking the file
For this, and to avoid you having to find the sfc_os.dll file for your specific version of Windows, this page will walk you through it using nLite.
- Start up nLite, and click next till you reach this screen:

Deselect everything except Options.
- Click next, and at the following screen click the Browse button and select
your Windows Setup Source.

- You should be presented with this screen, and uncheck everything to start
with:

- As we're dealing with WFP modification, check the following
option

- After checking the box, click the next button. Click Yes at the prompt to
start the process. It should only take a moment.
- Click Next, then Finish.
- Congratulations. You've completed and your Windows Source is ready to
install.
» If you wish to Enable WFP
Say you just wanted the ability to disable WFP, but still want the option to enable it, then it's as simple as setting a registry key and restarting the system.
The key in question is called SFCDisable, and is located at
HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Change the value to 0x00000000 to enable and to 0xFFFFFF9D to disable. The following are prewritten REG files that you could apply to your RegTweaks file, or import on their own later.
;Re-enable WFP [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon] "SFCDisable"=dword:00000000
;Disable WFP [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon] "SFCDisable"=dword:FFFFFF9D
» Final Notes
As you may notice, there are many more options within nLite that you can use. In fact, you could do the TCP patch, the WFP patch, and the UXtheme patch all in one step. This guide just breaks it up.
» Prepatched Files
Just select your operating system, download and replace the current file in your I386 directory, and then apply one of the above registry tweaks.