Occasionally a package updates a file in /etc/, and I can't remember whether the file was modified by me or not. This usually happens with things I don't completely understand and therefore don't know what I did in the past, such as PAM and libvirt.

Adding a comment to the top of each file I edit would help with this, but sometimes I edit files indirectly using utilities. libvirt's package recently updated ~30 files in /etc/ and I still don't know which of those were stock. I hope I got the u's and the z's right.

This feature, if implemented, would help immensely.