It is always advised that you do not re-freeze items once thawed. There are a couple of ways to get around this:
1. As Austinstar said, cook the whole batch and then refreeze the leftovers. That would be convenient if you divided it into single meal portions.
2. Get one of those frozen-food saws, they make quick work of cutting through frozen meat, cut off what you want and put back the remainder.
Of course, if you buy the meat fresh and freeze it yourself, it doesn't take much to freeze it in portions to start with.