Thanks for the link and the suggestion of how such a plugin might be created. It sounds a bit like the way the G'MIC montage works, whereby an image with many layers is formed into a single layer and saved to a file which must then be opened if further editing is necessary, only in the case of a "layer shuffler" the saved image would retain the layers, just in a new order. Currently I just import images as layers and shuffle them manually before applying the montage effect, which can be a bit laborious when the number of source images is large. I just created one with 88. Perhaps if I find myself having to create many more of these, it'd be worth me investing the time to learn how to author my own filetype plugin. Cheers🙂