As discussed with @rempt yesterday, I've modified Node.save to accept this InfoOjbect just like Document.exportImage in order to be able to save layers in batch mode with predictable output settings.
As it happens, I can't get Krita working with Python on my PC due to incompatibilities between PyQt5 (v5.11.3) & Qt5 (v5.11.1) libraries. It can't easily be solved as I couldn't find compatible packages, there's no PyQt5 v5.11.1 release unfortunately and the change appears in v5.11.2