Have you subscribed to your own BP ?As far as Im aware you cant overwrtite anything you are subscribed to.
If its your own just overwrite the original BP then update it on the workshop.

Originally posted by zaphodikus: Yep.
I have probably never "updated" a BP before and Empyrion is the first game I ever used Workshop with, so I was expecting a button to manually upload a file. Or that in-game the "update" button would be enabled. But it aint.

To update the workshop blueprint you need to overwrite the original file then update it. It will be marked with a little person & the workshop symbol smaller to the top right of it. like in this screenshot
http://steamcommunity.com/sharedfiles/filedetails/?id=862868321http://steamcommunity.com/sharedfiles/filedetails/?id=862868367I just uploaded something to test I can update the original but no what I have subscribed too.The update option is in the F2 menu
http://steamcommunity.com/sharedfiles/filedetails/?id=862870430

In your OP screenshot the one you have highlighted is what you are 'subscribed' too.Try going in to the F2 menu & finding the 'Zap-Runabout' & see if any of them have the little man with the small spanner icon & the Update box is selectable.The little man with the spanner is what you have published on the workshop.