Jo here I have a thing I worked one to get myself familiar with layering in Gimp and do something “productive” at the same time. It's a huge file to make new scenes for the first ritual (much bigger then the game in fact).
I used Upscayl to make the files from the game 4x bigger using the Digital Art preset and it worked fine. I got good results and tried to remove artifacts and reused a lot of assets from other scenes to spice things up but lost the grain effect from the originals (you can get that back with filters).
This “workshop” has a lot of different ways you can make scenes but still lacks some things I still could make (I like it gooey but there are few cumsplats so far).
Highlights are Bj with different dicks and a slightly different pose for fucking, also an option for eyes. See pics for examples.
For now I lost interest and don't have the time to get into renpy jet. If you want to make something cool for a mod feel free to use this. If you find something is missing feel free to ask. I can make new assets for this.
The pictures you export are huge and you have to reduce them to a usable sice for renpy, this makes them easy to manipulate without looking like shit.
Upscayl and other ai tools are a good way for modders and decensors to get good results without a lot of effort.
Sometimes I upscaled my own assets to make them fit in better with the rest.
Using this .xcf file will be taxing on your system and you should have a good setup also you have to figure out my organising (191 layers). Some assets have to be moved or are not in the order you want them. I used gimp, a free open source programm.
The way I see it you can get yourself 2-3 scenes out of this of varying escalation.
Mega
Good luck.