Is it possible to swap the sex event images already in the game for cuter* hentai girls i found on the internet?

*in my opinion

Depending on what you're trying to do, perhaps Docs/GenSex Image & Character Packs.txt will help? I believe if a mod provided files with the same name as the built-in image packs, the mod would take precedence. However, if you have fewer images than the built-in ones, you'd need to repeat your images, as mods AFAIK can't actually suppress existing files without replacing them.