Project vs. flow as xml export

Is it possible to export an entire project as one xml file instead of one file for each flow? I’m not finding this on my own. I did an edition of a polyphonic introit to which I had to add a different setting of the verse, since the original had none, and since it was technically a different work and for 4 instead of 5 parts, I made it a different flow. But I upload these to cpdl, and the assumption is that the xml file represents the entire edition.

If not, is there a way to join two xml files that does not require a computer science degree?

In your Dorico project you could copy the second flow and paste it to the end of your first flow. Hide the extra stave from that point.