So each team only has one field. So there is no way to put multiple fields for one team in one mod. With that said, all of my mods are in one package and you can combine elements from multiple field mods.
For example, Hanson edited alot of the goalposts (added Play Football to each one) and I didnt. So what I did is downloaded all of his preseason mods, applied them with Mod Manager, applied my field mods and then made my mods higher in priority.
So now I have all of my fields and all of his goalposts because my mod didnt edit the goalposts.