I had the same problem with integrating into my 4.12 Mod Act game, I tried to sort just winter stuff out but gave up in the end and just added the supplied static to the end of my existing one so creating a bigger mess in there than there already was, the maps did save though.
I do wonder how my ModAct install keeps going with the abuse it has had.
The objects supplied I just add into a existing objects folder I had specific to the map, topped it up so to speak, I will one day get around to sorting it all out.
Recently I went through all my skins, deleted the high res ones and any old stand in files for aircraft we now have and saved around 30 gig just in the one install, add that to my spare ModAct game and B.A.T and it was quite a saving in space.
Lovely maps all the same but I have to agree it would be better if the download only included stuff specific to the update to winter in objects and entries as it is so difficult to sort it all out and add to a existing static.
Take care and be safe.
Wishing you all the very best, Pete.