Sorry, I didn't notice how new you are to the forum (I had computer trouble for over a month) and didn't realize you might not be up on our "slang"
Civvie = non-diabetic kitty. ECID = Every Cat Is Different
Hermione is my diabetic kitty, diagnosed August 2016. Her blood sugar numbers are notoriously difficult to regulate
When I started feeding YA to my gang (I had 5 cats at the time, only Hermione is diabetic) I started with a small bowl of it next to each bowl of the old food. One of my cats loved it so much she went from bowl to bowl eating it all, then threw it right back up again

So I made sure to pick up the YA bowls when everyone ate until her excitement wore off. Once everyone was good with it I increased the amount in the bowl of YA and decreased the bowl of old food until it was gone.
My cats each have food bowls in different rooms, and I keep YA out for them at all times. My cats are all used to being free-fed, however, so if Buddy is used to eating only at set mealtimes I'd keep feeding him that way instead. Some cats don't show much change in blood sugar on YA, for others it causes spikes just like a high-carb food. Also the high protein and fat content can cause some cats to have stinky diarrhea too...
Kris is right, though. The
most important thing is that Buddy eats. In an ideal world our cats would all eat only what was best for them, but we all know cats refuse to obey rules

So we have to find the food that best works for their medical needs AND they will eat.