I, personally, don't refreeze any after thawing. However, I don't think you can cite USDA best practices for animals.
For example, my dogs will find the rottenest piece of dead squirrel/bird/rabbit that has been rotting in the 105 degree Texas sun for days and proceed to eat it with no issues. I used to try and stop them but I gave up on that as they never had any adverse effects. On is 12 and the other is 8 and they are both going strong. They like to kill squirrels and eat them over a period of days and then bring the rotting carcass in the house for me. It's sweet.
Now, I can't say the same thing for snakes but I don't think you can use USDA practices for snakes when those practices are set for human digestive systems.
Snakes will obviously eat dead animals since that is what most of us feed them so I don't think it's too far fetched to say they will eat deat animals in the wild as well and probably have some sort of defense against the bacteria involved in decomposition.
Having said that, it would probably be better to just throw the mouse away just to be safe.