Some people do it that way. I only combine milk that is at the same temperature- so if half of it was already refrigerated, I would cool the second half before combining & freezing.
I always combine my milk! I make sure it's about the same temp and dump it all into a freezer bag and freeze it! I probably wouldn't add warm milk to cold milk unless it's a tiny amount though. If you feel funny about it, I would just do the sniff-test before feeding your LO
I combine milk, however, I never combine cold milk with freshly pumped (room temp) milk. If I do want to combine them, I pop the room temp one in the fridge, wait for it to get cold, and then combine them (since they are both the same temp). Then I freeze them.
Re: Pumped milk storage...