I would drop the dose back, but how much to drop will depend on your comfort and your availability to monitor. Whatever dose you choose, my advice would be to test, test, test over the next few days. The data will help you know whether Cassanova's dose is too high or two low, and should shed some light on how far over or under dose he might be.
The number this morning wasn't bad, it was just a surprise. The fact that you just changed his diet makes things unpredictable, so reducing the dose is a good safety measure. Since he has done well on that dose for a long time, I don't know that you need to reduce by a ton, but there isn't enough data to say for sure.
Has Cassanova ever had ketones?