When I was breeding (bps, rats and asf) I started all my bps on live asf. 3 neals in they were switched to rats. 6 weeks f/t. Nwver had a problem switching once they got started on the asf. At that age once you get them going (in my experience) you can pretty much switch up their prey items without issues, back and forth, they pretty much go for anything. But if I started them on norway rats sometimes it took them a while to take their first meal. I mean, ultimately you want them on rats -but I found that as long as I started offering frozen by the 4th month (at the latest) I bever had a problem switching