The aim is to show the originally pasted URL next to the cleaned-up URL so that the editor realises that their URL has been changed?
In my opinion, because the current editing interface is good for me, I would just display the original URL in the same fashion as the current error messages, such as:
This relationship already exists.
These messages don’t mess up with the tabindex of keyboard navigation.
The workflow is the same as when there are no errors, so it is good. No additional keys, no additional clicks.
As it’s not an error, it could be a warning in yellow and not blocking, just informing that:
Original URL before cleanup: http://blabla.blabla/blabla?this=that