My first cat's bladder got fully crystalised and blocked up and needed an operation then the same special diet to keep him being able to wee.

When I was a kid, Science Diet wasn't around so the vet put him on a strict diet of raw chicken giblets and necks (with the occasional wing to give him something crunchy) and no bikkies. Poor thing was so depressed about it for quite a while, but he got used to it eventually and lived another 7 years very happily. Still used to run at the sound of any type of tin being opened.

I think your kitty will get used to it...cats are just generally slow to accept change, I think. He will soon learn that it doesn't mean that you love him any less.