Another way (without adjusting file permissions) is to get at the file is use the windows search for notepad, right click it (instead of left click) and select the option run as administrator.
As the notepad is running with admin rights you can then get at (open the file through notepad) and update/save the file without issue.
Just make sure to change the open file type from *.txt to *.* (view all files) or when viewing the folder with the wac files just enter *.wac into the file name box and hit enter, the wac files will then appear.