I was told that two snakes that I bought would only eat live mice and had been doing so for 2 years. The previous owner tried live rats and thawed with no success.

Rather than try to make changes twice, mice to rats, and live to frozen, I did both at once. I just didn't feed the snakes for a month. Then I offered mouse scented rats. Both snakes took them without hesitation. I did not pre-scent anymore rats after that.