Uremia in the case of kidney disease can sometimes present itself as a strong "urine" smell coming from the cat's breath. A lot of owners confuse this as being the cat's rear end or poor grooming habits. It concerns me that you're noticing this.

The vomiting can be attributed to the diet change, but vomiting can also be seen with kidney disease.

I strongly urge you to bring your kitty to the vet to be checked out. At 10 years old, kidney disease can be high on the list.