Thanks for the replies, I'll look into the tutorials for the normal model swaps to practice. I've noticed the tutorials say not to delete any CS_ files in the .imgs.
Swapped CS Gary with CS Santa...lets just say if you've seen the movie "The Thing" you'll know how horrific it looked
I also tried CS Gary to CS Johnny, Gary turns invisible
Also to many trys will mess up world.img even if you back up the original.