I smoke rarely, every few days I would have one. Would I be able to keep a good blood glucose/sugar level if I just have just one cigarette?

Your blood. Sugar depends upon thousands of things, most of which you cannot control. You can, however, control diet, exercise, risk factors, medication, monitoring, glucose control etc. Smoking is one of those thing you an also control. It's not up to me to tell you how much you can get away with before you have trouble, because it's impossible to state with certainty. Your choice. I can't give permission.