You could try to use the export as plain bibtex format. Alternatively, just create a copy of your bib file and open both, have one then in bibtex and one in biblatex.
Sure, but that’s exactly the manual task I am trying to avoid. Always having to keep 2 files current manually will lead to trouble further down the road…
Just to be clear: I get that Christoph’s suggestion will work. But it is not the feature I originally requested.
Many people will have to use bibtex, either for bibtex4word or as a Journal requirement.
At the same time, many people (like me) would like to use biblatex for their thesis or other documents they have more formatting control over.
So it would surely be convenient to always (automatically) have 2 up-to-date bib files in both styles without worrying that you forget to “save as” or “export”.