I would stick to F/T if thats what it has been eating IMO I wouldn't change to "live" to get it eating something else as it may prove a bit more difficult to get it back to F/T again.

Royals dont need rats and can do well on a diet of mice all their life if they will take them.

If he eats mice fine why do you want to change to rats ? he will be fine on mice I would stick to what is working ..