I have 12 out of my 14 ball pythons taking frozen consistently now, and one that takes prekilled off of tongs but not frozen. This is what has worked for me:

1. Attempting to switch them during the summer, when they all seem to have the best appetite and eat most consistently anyway.

2. Feeding small thawed prey warmed and dangled on tongs right at the door of their hide while they are inside. (Putting ball pythons in a separate container for feeding is often counterproductive.)

3. Some will not switch directly from live to frozen / thawed but will take prekilled that is still warm. I dangle it at the door of their hides on tongs for them to strike at. Once they have eaten pre-killed a few times, many of them will transition to warmed frozen presented in the same manner.

4. I have not had much luck switching young hatchlings to frozen and even seen my attempts result in them going on a "hunger strike" for a few weeks. Now I just wait until their first summer when they are approaching a year of age and are nice and chubby before attempting to switch. I have gotten a much better response from them that way.