Thanks for trusting me to help you and Riley today. I am a licensed veterinarian with over 30 years of experience and would be happy work with you.
Cats with IBD will often have flare ups and when they do, they most often are nauseous and don't want to eat. Trying to entice him with aromatic foods is a good choice. Even if he is still drinking, if he has not been eating well for 36 hours, he is likely a little dehydrated, so adding additional warmed water or broth to the food he is accepting may help.
If he is not moving around much, that may explain his feeling cold and eartips are going to get the least circulation (especially if his heart function is not that great). To monitor his heart disease, try to count how many breaths he takes in a minute when he is sleeping. If it is over 30 breaths per minute, it can indicate possible progression of his heart disease.
If he continues to ingest the new food, and his breathing is good, it sounds as if he may be stable until he can see your vet tomorrow, but if he starts to vomit or act lethargic, I would seek veterinary emergency services.
I hope this is helpful. Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please reply so I can clarify for you.
My posted replies are for general education only and not meant as a diagnosis. Only after a thorough veterinary examination can a diagnosis for your pet be made and specific treatments be advised or medications be prescribed.