Unfortunately, there is no quick and easy solution to your problem.
It is certainly not possible to change the way JuiceboxBuilder-Pro generates the SEO content code.
If the data you wanted to use for your SEO content code were embedded in the IPTC Document Title and Description fields within your images, then you could have JuiceboxBuilder-Pro use this information to automatically populate the image titles and captions respectively (using 'Images -> Titles' and 'Images -> Captions' from the drop-down menu at the top). The image titles and captions (sourced from the image's IPTC fields) would then be used in the SEO content code.
Perhaps you could find a program that would create a batch process to copy the content of the IPTC Keywords field into the Document Title and/or Description fields of all your images so that you could use this information within JuiceboxBuilder-Pro.
Otherwise, you could perhaps use a plugin (for example for Lightroom or WordPress) to create your gallery and then modify the plugin to generate SEO content code.
However, this would likely be a complex and time-consuming project.
You would need to:
(1) be familiar with the structure of the plugin you intend to modify.
(2) be familiar with the programming language used by the plugin (e.g. Lua for Lightroom or PHP for WordPress).
(3) create a method to iterate over the images in your gallery.
(4) extract the information you want to use for your SEO code from the images.
(5) output the SEO content (using the information extracted from the images) as HTML code to the web page.
How this would be achieved would differ greatly between plugins but the principle (the five steps above) would remain the same.