it's like this; any change to a char is like telling an artist painter to change a small detail in one of his drawings.
just, the game's editor is a painter who will create a whole new picture, for each change that is done to a char, no matter how small.
you want to add panties, well the whole char is redrawn, with panties. now you don't like the looks and remove them, ah okay; the whole char is drawn new, now without panties. it doesn't matter that -before- the char already existed without. it's created new.
would the editor store a -before- to every change on every char, i would quickly run out of HD space (right now ~650GB free) with only the 6 chars i have right now. adjusting skin colours 'just right' is tedious, since the result tends to look different in editor and fight (due to lighting influence i assume) which ends up me adjusting this or that by a one pixel at a time.