well, about the riggin, I tried it once, just with this game, but I couldn't check if what I did worked because I didn't know how to put it into the game. I had tried replacing one of the existing characters with "Unity Asset Bundle Extractor" but when it came to choosing it in the game, it crashed.
If you know what you are doing, maybe output_log txt will help to see what the issue with the crash is. It's in Yiffalicious_data folder.
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That's what devs themselves suggest users to send them. So maybe it can be of some help. But i don't know for sure, i'm neither a dev nor a modder.
You can also try your luck in asking the devs themselves, they are active on their discord server. YL1 Is probably a dead project to them, so maybe they won't be against your idea of modding their game. As far as i know they had no real problems with people ripping their own models from YL1 and porting them to SFM or using them in blender. So i doubt they are too anal about people messing with the contents of their game.
Otherwise your best bet is to find either a real Unity dev or an Experienced modder of Games made on Unity. People from this game's community
https://f95zone.to/threads/captivity-v1-0-5b-perveloper.66756/ have modded their game, it is also made on unity. I saw someone managed to add barebones custom level to that game, so if those ppl from their discord are still around maybe they could help you.
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obviously the UI will be more cluttered since theres way more shit that needs user input. Though I guess the options could be compartmentalized better. Creating masks is a bit fiddly for instance.
