The API export looks like this:
postdate="Thu, 23 Nov 2017 05:33:10 +0000"
editdate="Thu, 23 Nov 2017 05:33:10 +0000"
<body> [all the raw XML text with format codes, etc.]</body>
The only reasonable modification is the item itself, perhaps the name and existence. Would you need to edit the body text?
I'm playing around with name searches and bulk import of collections. I have updated bggcli to work in the modern era and have a gui for name disambiguation of searches.
I'm not sure what it would take to upload a new geeklist, as I would expect there is not an editing api, only reading. So any editing would be through the web interface.
I would need to edit the body text, unfortunately. I'm hoping for a way to not have to edit all the entries by hand to add/change/remove sleeve manufacturers.