In case someone stumbles upon this thread in the future, there were some unanswered questions.
In the folder where you've installed the game, there should be a "UserData\scene" folder with the scene files. The downloaded scene png files should be simply copied there.
You'll need a hexeditor for that. Open the characard png file, search for "【SVChara】" and replace it with "【HCChara】". Be careful not remove or insert extra bytes so not to change file offsets or any other bytes. You really must just replace the two characters in the identification string and nothing else (that's why I advise a hexeditor for this). Worked for all the cards I've tested with, but I can't guarantee that this will work will all cards (especially if they use lots of SV mods, this method will probably fail).
BetterRepack already has the "Free Sex" main menu option. If you copy the saved game included in the BetterRepack, you'll get threesome pose and all positions / places too.
The BetterRepack already has the full save in the "Extras" directory. Just overwrite your save files with those and you're good to go.
Yes,
You must be registered to see the links
(no login required, just click on the scene's image to download)
I believe everyone is using ScrewThisNoise's BetterRepack which has most of the mods pre-installed.