Thank you. The answer, unfortunately, is that it's impossible. The plugins draw the images you see using PIXI and are intended to preclude the need for any external images. The downside of that is that the images are not customizable.
Viewing post in Ten Mini Games for RPG Maker MZ comments
Appreciate the candid and timely reply! For me, creating games with commercial intent, it's important the imagery be consistent with the rest of the game. This is definitely something I'd buy if a future version (or different plugin) accommodates replacement art. Simplifying mini-games has a lot of appeal, especially being presented a handful of fun options that we'd otherwise have to wrap ourselves. Good work!