I can't remember if modded characters added to the recruits pool later on will appear in an existing game. I would expect that they can be as long as they haven't been triggered to appear yet, maybe the same for entities in maps (If not, could new recruits be used to carry the items in their inventory?). This sort of thing is quite a bit of work, so one would have to invest in reading up on how to do things.
But that's all academic really. THCola can survive without messing with the game, unless he has an interest in making something interesting and worthwhile.