You should not change the permissions on system folders and you should avoid changing system files.
Often, if you put the older/alternative DLL in the same folder as the exe (i.e. game) it will use that one instead of the one in the System folder.
If you must change a system file, use a tool such as PowerRun to open a Cmd prompt as TrustedInstaller. That will let you change what you want without messing with the permissions.
You also have to be aware of Windows File Protection.