In MY experience, and this is just my experience, mind you, is that either never switch, or switch often (every week or every couple days rotate between like 5 bags you have, and every time you buy a new bag, buy something different). Dogs are, infact ALL living things are (with lower life form exceptions) designed to eat a wide variety of things. LImiting your dog to 5 ingredients will cause his body to think t here are only 5 ingredients in all the world-- so when you randomly mix it up and introduce something else, he will have tummy issues.
Either never do it, or do it on a weekly basis to keep his system able to recognize and handle different protein and starch sources. I used to, when I worked at a feed store, bring home 8 bags of kibble at a time, and fed everyone randomly from a different bag every day, along with (healthy) table scraps like meat, fat, veggies or fruit, or fish. Even when one of my idiots got into the trash and ate an entire 8 lb tray of rotting and green pork chops, he didnt even have a fart.
You dont eat the same dish every day for your entire life, do you?