>>4451765
From what the description says it's substantial. From what I played (still the first Palace) it is still the same main story overall, but many details about kasumi are different from Joker. The major rewrites are mostly about her backstory with her sister and so on. Also a lot of her dialogue choices feel very different from Joker.
Of course Sumire feels like an entirely different Confidant now, because of obvious reasons. Honestly, a lot of the recontexualisations make Kasumi feel way more like she fits into this story than Joker did, who was even more of a blank slate.

If it's about the yuri, the dialogue with Ann really highlights the difference between her talking to a boy she barely met and another girl. I expect this to continue in all social links.

Overall don't expect to play an entirely new game and story, but it is way more effort than just switching models and pronouns. Also keep in mind it's a new mod with lots of room for improvement. If you can't handle occasional model clipping or wrong voicelines it may be too early for you.