The way Random originally worked when we released the software in 2014 was it just randomized everything with the same chance. We since made it more sophisticated, and there is now a chance associated with each layer, that determines how likely it is going to change. Most layers have a less than 100% chance, so this is why you are seeing some items remain unchanged between Random rolls. There are also several layers we decided to keep on 0% as we never wanted them to randomly appear.
Having a popup would be quite inconvenient, as if you wanted to randomize multiple times you would need to go through it each time, as opposed to how it works now, by simply pressing a button. Also, listing the categories by their names with checkboxes wouldn’t help, as they are sometimes represented differently in the actual config structure compared to how they show up on the UI buttons.
One possible solution I can imagine is converting the Random “popup” into a toggled overlay, similar to the Coloring panel, which simply lists all the category buttons and then use the active/inactive states to toggle if you want that specific category randomized. To get this done is a few days of work, and in all honesty, I can’t recall anyone else wanted the Random button to function in a more advanced way in the past 7 years. 🙂 So while I’d be happy to do it just for you alone, I also need to be able to fit this into my priorities. As I currently don’t yet have an upcoming patch scheduled for ePic, I also can’t tell if/when this could make it into the software. If I could find the time to do it, and also have other things that’d support scheduling a patch, I’ll definitely look into it.