Here is the skinny on this. I'm going to use my training in safe food handling to help. I also hold a food safety certificate. Even though this is a snake, you should handle and prepare its food with the same safety and care you would give your own.
As far as your pinkie mouse, everything is going to depend on how you handled the defrost and how long it has been defrosted and in the danger zone. When I say danger zone, I mean that temperature the is ideal for growing bacteria. The FSIS sets those temperatures in between 41F - 140F for a period of four hours. If your food item remains in that temp longer than four hours, then you need to cook it or discard it. You cannot refreeze it.
The only acceptable method of thawing raw food and then refreezing it is if you do it in the fridge or by using a method that ensures the food item doesn't exceed 41F or you cook it and then you can refreeze it. However, if you have thawed out a pinkie and your snake refuses to eat it and you have not exceeded your four hour time limit, you can put it in the fridge and keep it safely, for a period of one to three days. Bear in mind that before you use it again, you will need to use your nose and judgment to determine if it is still good. Just like any other meat, you can tell by look, touch and smell if it is still good. When in doubt throw it out!
Here is the break down
1. Properly thaw out the pinkie
2. Remember the four hour rule
3. The danger zone for the four hour rule is 41F-140F
4. You can save the food item, if your four hour rule has not been exceeded and you can get it out of the danger zone.
5. When in doubt throw it out!
Here is a link to the USDA FSIS website so you can check it out for your self:
http://www.fsis.usda.gov/FactSheets/Focus_On_Freezing/index.asp#top
Good luck and I hope I helped
Wayne