for Skyrim the modders went 3 folde whit the patch one that fixes all the game bug that Bethesda dint even with the final patch the outer one was replacing stock body mesh armours textures etc finaly adding via script exentder and plugins more content and options.
for SF2 so if then i dont if it possible i dont know a thing about programing maybe a plugin to fix and add stuff to the DLLs maybe for the avionincs etc as for model i still best his to make new models ourselfs like the upcoming Floggers pleople would still need to buy the core content of the game but cloud fix add more stuff from here in free manner!
my two cents
if a group like his was fromed you cloud count on my limited talents even if im not the more realible more modder around