I have always thawed all my rats and mice in the same bag. This Crosses the scents really well and I have never had a snake refuse to switch to rats.
I use hot water to thaw and heat my feeders.
I do this too. Well, I thaw overnight in the fridge and warm with water for most feedings.
Have had no issue switching BP's to rats but, both Carpets still refuse rats (one is now almost 6 feet and getting to be an expensive diner date due to his choice on the menu). The juvie Carpet with constrict and "kill" a F/T rat yet refuses to eat them. I must be missing something because she is in hunting mode 2 days after a feeding until I touch her with the hook or my hand depending on where she is.