Similar, if you can get a population to reduce their consumption by x%, it doesn't matter if that's because x% went totally without (and the rest didn't change anything), or whether you could a more uniform, mild change.
Convincing people to give up some meat is pretty straightforward: one proven way is for meat to become more expensive. People react to economic incentives on the margin after all. Other ways might be to make the alternatives more appealing.
(About the margins: meat would have to get extremely expensive for many people to completely give up on it. But if sometimes you are deciding between going to a steak place and a pasta place, and then price can sway your decision fairly easily. The meal at the pasta place can still have meat in it for this example to work, just less of it.)