It will fire up and run fine down to about freezing. So it's only really necessary to change it if you are starting the tractor a lot below about 25F. And it's going to flow about the same at those temps as the multi-weight at least down to freezing - nothing to be gained. Now if you ARE starting it a lot below 30F or 25F, then change it. You can just drain it out cold and refill with enough 10w-30 and not worry about heating it up and doing it 100%, that will be enough.
Here in western wa where it rarely gets below freezing, we do not change the oil for winter and do not worry at all starting it in the few days in the 20s when/if it does snow duty.