I just recently moved from Windows XP to 8 so I'm pretty much new to setting permissions for directories in Windows 8. I'd like to know if I make a change for permissions to a directory in Windows 8. Can I reset them to their default? If so, how?

For example: I tried to change the permissions of Windows 'Temp' directory just recently, how am I going to reset them to their default?

Not an answer to your question, but whatever you do, DON'T USE OLD XP PARADIGMS AND HABITS in Windows 8 (or Windows Vista/7 for that matter).  The OS is based on a completely different architecture and has different ways of doing things.  If you have not used Windows Vista or Windows 7 for any length of time, tread slowly and lightly taking time to truly learn the new OS and how to do things within it.  You will be much better served and happier in the long run.

Back to your question, it is best to not change the permissions of any system directories.  In the case of C:\Windows\Temp, that is now considered a system directory.  If you really need access, open an administrative command prompt (right-click, Run as administrator) and navigate there.  The built-in, local administrator account has full access.

As of the Windows version 6.x.xxxx family, the default temp directories are %temp% which is %USERPROFILE%\AppData\Local\Temp.  C:\Windows\Temp is strictly used for Windows' only temp files.