This trick is certainly saving me an enormous amount of time so I recommend it to anyone else for whom it works.
It does seem to work on Macs running on Sequoia but I don't know if it works on other systems.

I see now that you are opening the 'Images' panel in JuiceboxBuilder-Pro, deleting the existing images there and then adding new images in the user interface.
I thought you were manually opening the gallery's 'images' folder, deleting the actual image files there and then adding new images into the folder using your Mac's Finder. I think I was thinking that because I remember recently pointing you towards the manual method of creating a gallery in a different thread.
Your method is a lot less unorthodox (and a lot less time consuming) than I initially thought!
I'm glad you've discovered a method that saves you time. Thank you for sharing!

I multi-select all the new images (I normally do this in Bridge) and drag & drop them onto the "Drop Images Here" spot in the Images panel. The thumbnails just build from the Images and Config sets itself.

I actually already have deselected both the 'Resize Images' and the "Crop to Fit" checkboxes on the 'Images' panel.
I have kept image size at 1024 x 768 but they are coming from Bridge with the long-side at 2048 px before they are automatically resized in JB.
If the "Resize Images" is selected then the images do load at a truly glacial pace

This is a link to one gallery which I built using my very unorthodox trick:
https://shelbourne-america.net/Terracot … index.html

I don't know if you can download the gallery from my website but I could let you have the whole gallery if that would help.

If I do this (manually replace the images in the 'images' folder and click 'Save' on the 'Publish' panel), JuiceboxBuilder immediately reinstates the original images (as I've bypassed the 'Add Images' routine on the 'Images' panel and JuiceboBuilder has no knowledge of the new images in the 'images' folder).

Are you manually adjusting the 'imageURL' entries in the gallery's 'config.xml' file (to reflect the new image filenames)?
How are the thumbnail being generated?

Maybe I'm not following your instructions correctly.

If you don't need JuiceboxBuilder to resize your images, then you could deselect the 'Resize Images' checkbox on the 'Images' panel. This should speed up the 'Add Images' process a little.

When making a new Gallery, open this one;
insert a different name and then, in "Publish", choose a new location in which to save it;
and hit SAVE.

Now open the new file; go to IMAGES and delete all of the existing inhabitants.
Then drag and drop replacement images into their place and, in "Publish", hit SAVE again.

Refine the gallery names in the resulting new Gallery and insert an updated Splash page etc.,
and Save again.

I find that by doing this, the new images insert themselves at great speed instead of the glacial pace that is normally experienced.

Hope that this idea will prove useful!