If you're concerned about them no wanting it anymore, I wouldn't. It's technically different every few weeks! You're adding more raw/less canned. Voila! Different food.
You could also do as AC has recommended by adding bits of freeze dried liver/chicken/fish treats, fish food, etc to entice the picky one. AND! Once you get to the meat chunks level you can keep it interesting by adding new meat all the time! Our cats have had goat (didnt like it), rabbit, quail, frog, fish, moose, deer, mice, rats, chicken, goose, pheasant, turkey, beef, pork, lamb, and we're hoping every so often to get more exotic meats. Never boring here! (although, the majority of their diet is beef heart - they will NEVER tire of that stuff)