I forget the exact moment but late on there's a point where Kyle comes at you ready to fight you, and you have the option to "fully bimboify and forgive Kylie" or something along those lines. I forget if it's even a forced event on one of the last couple of days or if it's one of the events you have to select during "free time".
I know all the times I've done it has been when I've also previously taken Heather and Nikki from him, so him coming after me to fight me is justified, and obviously I've also previously bimboified him when I had the chance as well, and I always play with cheats on, so I'm not sure if that will change things for other people.
I'm sure someone else will come in with the exact day and time, though, but I hope my answer helps at least a bit lol