Heard it all before.
Some people say stick with one thing when you know it suits and do the taking away if not eating thing. This has to be done if your dog's tum gets upset.
However mine are ironguts, so I indulge by ringing the changes. When we finish a sack of dried , we have a few weeks on tinned, usually Butchers. That's Izzy's favourite , anyway.
Picky Izzy will readily eat Butchers, Pal (usually) and Chum. Dried he likes Pero Gold (mainly the pasta part), Pedigree, but only for a few days and Vitalin ( can't remember whether Supreme or Premum, but the one shops don't stock, so it comes from shows).
Barbara, Monty, Joly and Teddy.