Units can't be directly transferred from game to game (although their models & textures probably can)
Not doable.....The game calendar is stricly limited. However don't let this stop you, most players will happily ignore the game calendar if the scenario (& its briefing) is convincing enough.
You could import snowy ground textures and I believe the temperature can be set to freezing, but the weather options like the calendar are stricly restricted (this is why the 'H&E Mod' doesn't have rain).....I don't recall snow being an option in CM:BS (but it might just become available in a future module).
