In the config file at

you will find lines that define the function of variety. Variety is a wallpaper changer and will also give you new wallpaper from the standard sources or you can add more personal sources.
More information about variety in this article.

You can add any program with extra parameters and execute it.

Variety preferences is set to floating.


Another example in this regard is the scrot line.

A tutorial to show you the code in the config file.