The pages from the manual above, along with my reply, explain how to add info to the XML file. If you only want to add info to ONE of them, you can press the Edit button in the Extended Details panel and add the information there.

If you want to edit one or more, there is a Python script (screen shot shown above) where you an edit one, or all in a folder, or all in a runtime. The easiest way to do it is to change all of the COMMON information first (like creator, created date, product name, etc), and then edit the UNIQUE info in each file afterward.