i think one could generate the background first and then the characters separately on a different layer, so any editing only affects them and not the background

Edit: just tried it and it mostly works. Generate background, then add pose, add new layer paint on top of pose, select area around character and click generate. The caveat is that it also generates a bit of background around the character, but it does not change it so dramatically

Elsewhere in the video they limit changes to a specific region - I wonder if that works currently with the pose changes.