Yes, I'd try 8.5 units tonight, unless he's really bouncing high by shot time. In that case, you could shoot the old 9.0 U dose one more time and go to 8.5U tomorrow morning. We call that shooting through the bounce. Again, the 0.5U reduction is a bit of an experiment. It's what you increase with at this point, but some kitties are sensitive to even .25U changes, so you may find 0.5U is too much of a decrease. But with the larger doses and larger depots, we are a bit more cautious at first.
Another technique sometimes used with larger dose cats is to do a reduced shot for one cycle (say 1/2 or 2/3 of a dose) after a reduction is earned, to help drain the depot. You don't want a larger depot to get ahead of you. But since Tennie came up pretty easily from the 40's, and seems to be staying there, you may not need that trick. But let's see how the cycle plays out.
I find with Neko that the HC food lasts about two hours, then the numbers begin to wobble down again. Depending on the cat, some acros have working pancreases. Which means that if you feed low carb food it can stimulate the pancreas and bring numbers down. Not something you want if numbers are already lowish. Just something to keep in mind. With non-acrocats, people will feed some LC in greens to encourage a surf. It may or may not work with Tennie, you'll have to experiment and see what happens.