Culture can be changed indeed, as can be seen in religion where branches has happened and whole demographics has gone and switched to different religions.

The reason for the decrease in smoking is still being researched and debate, but the main arguments that I have seen is the main role of smoking as social stress relief and as such it has been replaced by other addictions like opium use (mobile phone use, social media, and games has also been argued).

If we consider food culture to be malleable, we definitely should move to aquaculture as a main source of nutrients. Farms on land compete with forests and human activity, and land based farms uses artificial fertilizers (derived from natural gas) and massive amount of fresh water. Shellfish, invertebrates, and seaweed can provide both protein and calories, and has the lowest environmental impact of anything we eat today and can even have a positive environmental impact if farmed correctly. Changing farming from doing harm to doing good would have massive impact, and all it takes is a cultural change.