Wether you do it overnight or over a decade you have the same problem: you go from feeding 3000 people per acre to only feeding 1500 people per acre. Unless you have half your agricultural land unused, can create more arable land (difficult to do quickly and long-term), your economy can afford supplemental imports in perpetuity from trusted sources that would never put political pressure on you some time in the future, or you can convince your population to starve or die off willingly, you’re going to have a bad time