Using the technique of editing in photos editor worked fine, except for the fact that clicking done in the photos editor after my affinity edits caused photos to completely replace the edited photo with another random photo in my photos database. IE
1. open photo to edit in photos editor
2. open affinity using "..."
3. Make edits
4. Save/close in affinity
5. Edited photo appears in photos editor
6. Click done
7. Boom - a completely random photo appears in my album instead of the edited one.
Now it just happens that the two photos have the exact same filename.
I suspect an apple photos bug but who knows
