Many of you already know this but just to reiterate something that I have found to be really really helpful (did not always know this).
When "creating a similar listing" (new) and all those images from that listing show up (but are not applicable to the new listing you're creating), CLICK on anyone of the images. When your group of images come up, they are, of course, numbered. Go to the top and click on RESET, than proceed to choose the images you want. When DONE, they will automatically replace those that were there. Instead of removing your Header and Gallery Image, JUST do the drop down and choose the # you want, it will also replace.
This is "ALMOST" as good as what we are all asking for. You just have to REMEMBER to do it. Hope I was clear in explaining.