Brush thumbnail creation - option to clear scratchpad but keep icon

Currently, there seems to be no way to load an icon on top of the scratchpad. As a result, if my sketch is flawed (i.e. overlaps the icon), I need to clear the sketch and this also clears the loaded icon.

I would like to load the icon on top of a sketch and not have it clear the contents of my sketch. So basically, there would be three layers that would be flattened upon saving (from front to back):

  1. The background
  2. The scratchpad’s contents
  3. The icon

And I would like to clear the scratchpad’s contents and keep the icon.

mostly i create icons as a new file. though i could see ceating it a different software could be easy too.
then import and add the final brush stroke to it.

in krita i would like to open folder where icons are located from that window. so i can add more icons to it. more transparent background brush tips and tiny icons.
as well as be able to make the background any solid color.
and being able to have like a few brushes that i can use just from there aside from the main brush in question.