OK... I wrote the PHP code and was able to replace two more editor toolbar images with Font Awesome icons (getting round the issues with the original QRE plugin code). The main icon left to do is the "code tag" icon, but I'm not inclined to replace that one yet, since:
- it is not easy to find a replacement; and
- it is also embedded into may "info" and "hint" areas of the site.
Next, when I have time, I'll transfer and test the same icon changes for the "advanced " editor to make the icons consistent across various site editors.