When using the Lightroom plugin, all options are intended to be set via the interface.
Default options are stored in the 'galleryInfo.lrweb' file which is compiled and cannot be modified but if you change any settings in the interface, they should be remembered the next time you open Lightroom.
If you like, you can override the interface and set a value to be used in all galleries by modifying the 'config.xml' file in the 'juicebox.lrwebengine' folder.
For example, to use thumbnail dots in all galleries, change:
useThumbDots="<%= model.nonCSS.jb_useThumbDots %>"
... to:
In this example, the 'Use Thumbnail Dots' checkbox will be ignored in the interface and useThumbnailDots="TRUE" will be used in all galleries created by the plugin.
how should one use the entry box for Pro options
Please see Step #4 in the 'Upgrading to Juicebox-Pro' section on the Lightroom Plugin page.
I tried, for instance, to set the background color through config.xml but it didn't work; it appears it needs to be set in the UI.
The background color can be set in a gallery's XML file but because the plugin sets the background color in the embedding code (as in our example code here) it overrides the value in the XML file.
The order of option precedence can be found in the Setting Config Options section.
If you want to set a background color for all galleries, open the 'juicebox.lrwebengine/index.html' file in a plain text editor and change:
backgroundColor: '<%= rgba(model.nonCSS.jb_backgroundColor_, model.nonCSS.jb_backgroundOpacity) %>',
... to:
backgroundColor: '#222222',
... changing the hex color code as appropriate.