Hi Nik,
I use actions in Photoshop to replace the background, basically Select Subject and then Replace Unselected with 230,230,230 or whatever the customer specifies.
So once I have selected the images to go to the customer I put the original JPG files in a folder and use the Batch process in Photoshop to do them all at once, then put them back in the original folder.
Then I go back to the catalogue (Aperture, Photos, Raw Power) and hope to see them ready to go.
Aperture detects the original has changed and starts processing by itself and they come up as you scroll through them. Photos and Raw power don’t seem to detect the change.
The work around at the moment is to create a Preset that changes to the Clarity from 0 to 0.1 and then they all re-render.
I think to use an external edit process on each would be too slow and just create an unwanted extra file.
Bob