>>/813/
Hmm, I am not sure there is, I am afraid. You can manually jigger rechecks for URLs when the file is actually at the URL, but not a 'get the tags from this URL and apply them somewhere else'.
My current prototype for fetching tags as suggestions for files from individual booru URLs is the 'file lookup script' system, which you can turn on for tag suggestions and can do some iqdb stuff. I was never really happy with the first version of this, but when I update and expand it in future, it would be nice to just be able to say 'hey, grab tags from this URL and stick them on the clipboard' kind of thing.
I will keep this in mind.