Override an Admin file?

I'm making a small change to admin/packingslip.php -- is there a way to override that file, or do I just make the change directly (and hope I remember what I changed when I upgrade)?

At this time, there is no override system for admin files.

Ok, I think I'll keep a log of my customizations...

When you upgrade, simply use a merge tool like WinMerge to very quickly identify all your customizations. You can use that information to rebuild or adapt any of your customizations into the newer version you're upgrading to.

When I override something that's not part of the override system, I create the custom folder and store a copy of the changed file in it anyway. It won't be used by Zen Cart, but it won't be overwritten by future upgrades/updates, so I can always use it to make the same changes in the newer version of the file (which I'll then use to replace the old file in my "custom" folder).