Hello hippophile1 -
You are most welcome. There should not be any issues when changing the images for your new listings. If you make alterations to the HTML directly it is possible to affect the gallery code which can create issues with the scrolling gallery. If you are modifying a listing within your Auctiva account and make text changes using the editor without going into the HTML you should not encounter any trouble. If you have more than one listing active, the gallery should show appropriately on your active listings as per your gallery preference settings within Auctiva.
If you refer to changing your header image on an already active eBay listing, you will need to let us know that you have done this once you are complete and we can run a command to ensure that the images in the scrolling gallery update accordingly.