Thank you for the quick response!
I think Ctrl+Left Click would work great, thank you!
I was picturing an external drag & drop at first, but I think I get the problems with both. I think flexibility would be preferable so long as there's specifications for the dimensions and whatnot in the README file.
Perhaps after importing sprites, there could be some sort of "save template" function where someone could name a group of settings (for example--in "Template 1", use "x" custom sprite for Simon, use "y" sprite for floor tile, use CM defaults for everything else) that could be accessible and reapplied once the program is opened. The function would search through a specific import folder for the custom sprites. Again, I'm not sure how well that would work or if it's the best option; I just appreciate the opportunity, haha.