"Should Governments create laws that enforce vegan principles in order to combat climate change?"
Should governments attempt to create laws that would attempt to enforce vegan principles to combat something that's been occurring long before the dawn of man, in order to try to combat naturally occurring climate change, it would fail quickly. The majority of the world's population eat animal products of some type, with much less than one percent following, or trying to follow the vegan principles. As such those trying to enforce a policy would quickly be overthrown within a matter of days, weeks or even months. Even many vegetarians would stand up against such an attempt, especially those whose diet includes one or both dairy and eggs. Then there strict vegetarians and vegans, who realize that there's no such thing as a one type of diet, that will work for everyone. Then add in those who realize that climate change has been occurring since before the dawn of the first primate. Then you have those who would realize, that to create such laws, would only be the beginnings of affecting their rights, in other areas beyond diet. Then there are those who are aware of what's known as failure to thrive on some type of even the most diverse and realistic strict vegetarian diet. Those who are aware of it, has either done their due diligence, or seen people suffer from it in person. That includes those who did everything they could, to make even a lacto-ovo-vegetarian diet work, by excluding nothing beyond animal flesh.
Also there are vegans and vegetarians who are well couched in paleontology, who knows that the earth has undergone climate change since the formation of the planet, more than for billion years ago. They would consider that to be a folly. They know about our planet's axial wobble, and that it impacts the climate on a cyclical basis. Laws any government could create to try to enforce vegan principle to try preventing climate change they'd point out would have little if any real significant impact, both short term and long term.
Then there has been over the course of time not just major ice ages, but also minor ice ages prior to the existence of man, but also some minor ice ages as well, which mankind had no part in or the ability to affect it one way or an other. So trying to create laws to enforce vegan principles, in order to combat something that man can not control, i.e. climate change, is nothing more than an exercise of futility.