Don't worry about the highs from bouncing. Some cats will bounce from yellow and most will bounce from perfectly safe blues if they aren't use to them. An increase dose will mean lower numbers, but could still be very safe numbers. Yes he will bounce to those "new to him" lower numbers, but that's OK. Seeing those lower numbers is the only way he'll get used to them.
You've done enough testing, even after the fur shot, to know he needs a 0.5 unit increase.
Typically with a dental you will shoot a half dose the morning of the dental. Depending on what anesthesia induction drug the vet uses, it may or may not have a BG lowering effect. I suggest testing when he gets home that day, and then at PMPS. You might want to be cautious if he's coming down to PMPS. However, given the high numbers Yoshi is in, it's likely not to be a worry.
If there are extractions at the dental, or even if not, there is likely to be some inflammation that will keep the numbers higher for a while. I found it took something like a week and a half before Neko's numbers showed any change.