Slut level is equal to the number of passives. Changing it wouldn't do anything good because game will just calculate and correct it again.
Also, I don't think it is all about slut level.
I think slut level dictates how she reacts to sex attacks(blowjob, vaginal etc.) and other forms of harassments(such as being petted, dirty talked to, masturbated to etc.)
But that's not all, there's also her sex skill levels, such as handjob and vaginal sex. Their levels change her dialogue while using them.
Like I said before, it is better to just either lose the game on purpose or just restart again if you really want to see it all.
Actually, there's another way. You could extract audio from game files. I did this a long time ago, I still keep some of them for personal entertainment reasons