Welcome to the forum!

To answer your questions, Balls are imprint feeders and typically stick to one type of meal all of their lives. Of course there are exceptions and you may get him to change if you work with him, but he might be more finicky if you change his diet.

Your best option would be to continue feeding him 2 live mice every other week as that is what he's used to. He will do just fine all of his life with that schedule. If you want to switch him to rats or to F/T it may take a little work, but it should be possible. The key is to go gradually instead of trying to get him to eat F/T rats right away. So either try to get him on F/T mice or live rats, but not both at the same time.

If you want to get him on F/T mice, try feeding him one live mouse and then offer him a pre-killed mouse right after using tongs. If he takes that, then you can try offering him pre-killed mice on tongs after a couple successful feeding attempts. After he is used to eating pre-killed off of tongs, then try F/T.

If you want to get him on rats, try adding a little bit of soiled mouse bedding about 20 minutes before introducing a live rat. The rat should be about the size of a mouse or a little larger. Eventually you can work you way up to a small or weaned rat which is about twice the size of an adult mouse.

Oh, and one more thing... if you're feeding him two mice, let him consume one completely before offering the second one. This will reduce the chance of him getting bit or spooked by the one that isn't being eaten.

Good luck!