I have not seen any posts about this, so thought I would post here.
So if you want to edit or add a smart stack, you need to more or less edit it and remove or rearrange the existing widget options there. The only other option is to either smartly rotate through them all day or something similar.
I have found a way to create your own smart stack where you can select and select the widgets you want to display. Basically, you add whichever widget you want on the home screen and drag one on top of the other. The most important thing is to make sure they are the same size. You can have as many or as few widgets in rotation for your custom smart stack.
Sorry if this was already discussed or general knowledge, but I have not found anything similar online, so thought I would make a post about it! Hope this helps and hope you have a wonderful day!