Yes this will be a major problem. Also a major security concern.
The only clean way of reverting the change I can think of is to System Restore to the point before you made the change.
Another way which is not as clean but could be an option if you don't have a restore point is to use icacls.
First find an unaffected machine with the same version of OS and run icacls to save the permissions of the entire tree under
icacls c:\windows\system32\ /save FreshWin32Permissions /T /C /Q
Then copy the file you created into affected machine (via network or USB key) and restore the permissions by running:
icacls c:\windows\system32\ /restore FreshWin32Permissions /T /C /Q
For more info on the method above please check this post:
This also reminds me of "I accidentally ...". I hope your post is not one of those jokes.