Hello!
I drive my 2000 Mazda Protege (120K miles) 5 miles one-way to work (combined 10-20 miles a day, 50-100 miles a week, depending on lunch hours.) My commute is on interstates, so I get to drive at speeds of 50-60 and also at low in-town speeds.
From what I’ve read, it looks like I should get my oil changed once every 6 months. My question is, I live in MN and we get some pretty cold winters. Does the every 6-month rule change when taking into consideration the cold weather?
Thanks in advance for any and all advice. 
Yup.
My opinion: the manual says every 3K, and there is no time limit. I have seen mechanics trying to sell the fact that if in 6 months you have not driven 3k, change the oil. That is a porfit to them and a loss in the pocket to you.
On most of those trips the engine won’t reach full operating temperature, or if it does, it won’t remain there long enough. This will lead to a buildup of moisture in the oil (water is one of the by-products of combustion so it’s unavoidable). Personally, I would change the oil twice a year: right before and after the cold weather sets in. That should be sufficient for your driving pattern.
Most “severe conditions” maintenance schedules say that you should use them in extreme hot weather and extreme cold weather. So cold weather might mean more frequent maintenance. Check your owner’s manual. Read it from cover to cover.
NYBo has the right answer. Getting your engine (and oil) up to operating temp gets the moisture out of the oil. Moisture naturally gets in there as the engine cools. It’s normal. In addition, there are acids that can build up if the oil is not brought to temp (part of the whole moisture deal). Having lived in MN before (way up North), on such a short commute, if you get the oil chained in November and change it again in March/April, you should be ok. Once a month, you may want to take it for a drive to get it up to operating temp for a bit.