Lock files and folders in Mac OS X
You can easily prevent changes being made on any files or folders in Mac OS X by locking the file or folder in question.
* Select the file or folder you want locked
* Go to File > Get Info (or hit Command+i)
* Under ‘General’ click the ‘Locked’ checkbox
Close out of Get Info and the file/folder will now be locked, preventing any changes from being made to the file. If a file or folder is locked, it will also cause an alert dialog to popup if you try and delete it, saying “Item ___ is locked. Do you want to move it to the Trash anyway?”
You can unlock a file in Mac OS X by reversing this process and unselecting the checkbox next to “Locked”, although if you are trying to unlock a file that you do not have privileges to you will need the admin password.