But that would change it for all current users who have not overidden the 'default, which I imagine is most users.
In my experience most users don't like (resent) user interface changes, because they have to do something (e.g install 3rd party products Start Button 8, Classic Menu...) to get back what they had. In this case they'd have to find the current icon and override any replacement.
I appreciate most users probably wouldn't, but there's a principal at stake here; making an unnecessary change at the install level... unnecessary, because the wherewithal exists to make the change at the user level... would set a precedent, and 'usurp' the simple but very effective resources override scheme that the calibre developers have provided... if only other software had similar facilities Ψ²
You should have raised this when the editor was in beta. That's when I changed the save.png and document_open (to my eyes the default looks like a printer) icons, which are in fact the only icons I've overridden
Feel free to use this orange save.png
BR