First of all, good for you for wanting to feed your cats raw! They will thank you with good health and happiness. As for freezing and refreezing, nothing wrong with it, although it might be easier for grinding purposes if the meat isn't completely thawed (gets really gummy when it is). Have you seen this website on making your own cat food?:
http://www.catinfo.org/makingcatfood There's a ton of very detailed info there. Let us know how it goes!