Can I rerefrigerate thawed breast milk which baby completed drinking half way?

This is a definite no-no! This is because once the milk is thawed to room temperature, the room temperature promotes bacteria growth in the breastmilk which may be harmful to your little one. What I did was to store my breastmilk is 80ml bags instead to minimise wastage instead of filling the bags up to maximum capacity. Sure, it may seem like wasting breastmilk bags, especially if you're using disposables but I was a low-supply mummy so every little bit of breastmilk that I could save, I would save. http://kellymom.com/hot-topics/frozen-milk-power-outage/