I'm in Houston, and temperatures have been bouncing between the high 70's* and the 40's*, with a hard freeze thrown in here and there. Most years, it's fairly temperate.
My fish seem to want to eat most of the winter, at least when it's in the 50*-70* range. But I feed them less. If it's really cold (40's*), I'll stop feeding 'til it warms up. There's usually enough algae to be found in the pond that they can keep themselves satisfied 'til it warms up. Mostly, when it's cold, they don't move much, and therefor don't burn many calories or need much fuel (food).
I still clean my filter each week. I find there is enough gunk accumulating in it, partially due to fish poop, but also leaves falling and decomposing, etc. And, two weeks in a row, leaf debris has slipped past the pre-filter on my pump and caused partial clogs, so I've been taking the pump apart each week to clean it, too.
I don't know about the water change. Seems like too much stress to me, on fish who are already stressed by cooler temperatures, and not at their peak, due to being cold and semi-dormant. They're also not eating / pooping as much, so they're not creating the toxins that are the reason for water changes in the first place. I would hold off on that.
