Why make the switch at all? If the snake is happy and healthy with mice, then keep him on mice, though a full grown ball will need more than 1 mouse a week. 2 of my balls will only eat mice, while 1 will only eat gerbils. None of them like rats, so I don't force the issue. All are very healthy, good weight and my oldest is 15+ years old and my other 2 are over 10 yrs. The 2 on mice now, were once eating gerbils until they decided they didn't want to anymore. They refused to eat for months, until I wised up and went back to offering them mice! They gobbled them up like kids in a chocolate factory. Point being, your snakes know what they want and need, its up to you to provide it.

Tough love may result in the snake just refusing to eat period. We all know how finicky BPs can be about eating. I'm not saying don't try and offer your snake some variety, but I wouldn't agonize over it. Give them what they want, live, frozen, or whatever they want. Make life simple for yourself, and your snakes.