Ranma and Shampoo living each others lives maybe interesting but this idea is too disjointed for me to really follow. I don't really know what the idea your trying to present is beyond Ranma and Shampoo somehow switch bodies.
Ranma can't speak Chinese.
Ranma spent enough time in china that he most likely can speak some Chinese maybe not the Amazon dialect though.
Ranma can easily mimic all of Shampoo's techniques with the exception of the remote control acupuncture and mind wipe.
Ranma...can't hit girls.
Ranma will hit girls. He hit Shampoo to win the contest. Was going to hit Kodachi with his hand but rules forbid it. Hit martial arts cheer leading girl. hit konatsu when he thought konatsu was a girl.
Wouldn't Ranma's fear of cats and Shampoo turning into a cat be a major problem to this story?