The first answer you suggest is definitely possible. You can scurry a Kypiq down to your duchy and then marry it and will some titles around, and eventually have a kypiq Dynasty. Quick clarification though.
You can't delete characters. You have the ability to spark out of a character, but then it will continue living as an npc for the remainder of it's life. Whether that means you have to will your title and then off yourself or wait for a natural death, or if you could will your title away while remaining alive I'm honestly not sure. I've never seen it suggested you can give your title away while still alive, but it would make sense to me.
The second option, much harder to accomplish. You can in fact, over the course of KoE, translocate a population of kypiqs into the county you want. But it has been stated prior that you simply won't be able to get a majority this way. Maybe if it was really close, like 51% neran, and 49% kypiq, you could tip the scales if you had a buddy or two help you, but for your scenario it sounds not likely.