You have an 04 Ford and I assume it's diesel since you're asking about diesel additive, the answer would depend on where you are. Your profile says New Mexico. I have an 05 Ford 6.0 diesel and am in cold weather all of the time.
Here, they sell #1 from late Sept (usually) on. However, when headed up the highway to go moose hunting in mid Sept when it can be down to 10* F, sometimes #1 is available and you go with what you can get. I can't say I've had any problem running on #2 diesel in that weather.
When the fuel supply switches to #1, I start adding Power Service (in the white bottles, not the grey or red bottles) when I fill up primarily because the refiners take a lot of the waxes out of #1 fuel so it lacks lubricity to lubricate the fuel pump and injectors. A lot of new people up here loose their fuel pumps and have to spend big money to replace them.
I don't think you need to worry about it.
Bill