There's another "hidden in plain sight" feature for documenting changes.
Every time you write your project to the PLC, the "Download Project to PLC" dialog has a small text field where you can make a note of what you are doing for THAT specific download. It's optional. You don't have to enter anything. But if you do, it PREPENDs that specific download note to your Project Notes document written to the PLC (it marks the text entry with current date/time and the current user that is writing the project to the PLC; see attached screen shot).
You can view your download history in this Project Notes document from the Dashboard (see Documentation panel, View/Edit Project Notes hot link). It's just text, so you can tweak it - you normally would not, cuz you really want it to be a log of all the downloads - you can also print it out as part of Print All. See other screen shot.
Note that the Write to PLC dialog PREPENDs each entry to the file, so the most recent one is AT THE TOP and the oldest is at the bottom (note the auto-generated timestamps and user name).