it's a bit more complicated for characters models and you most likely have to redo the whole extraction/convertion from scratch.
Another user was trying to convert them for TBC from my patch but got problems with the missing belt (a geoset I had to remove for vanilla and seems to be used in BC). Basicaly he got holes in the models.
You also have to do all the dbc convertion and add the missing npcs and their textures which is quite a bit of work.