If they're scored, I don't hesitate to cut them in half. But if they're not, I assume there may be some reason for that. For example, they may be erosive and they're coated so they don't eat up my esophagus on the way down. That's just one example and oversimplifying, but the implication is pretty clear.
Regarding dosages, I like reading the studies, but I usually go with what the doctor and I agree on. Sometimes, we adjust the dosages after trying one on. Maybe I need more or maybe less. But I'd prefer to base that on my own bloodwork and tests. We did a lot of adjusting and optimizing in the months after my bypass surgery.