Changing save difficulties mid-game?

Hi guys. So, I have a really nice wall that I want to get built, but it takes about 284 logs to make, and whenever I try, first I’ll get swamped by Entlings, and then my value will go through the roof and goblins will spawn. Is there a way for me to start in peaceful, get my walls up, and then go back into normal? If not, I’ll just play it properly and actually have some soldiers before building the great wall of Trumpia.

To avoid the ents you need to avoid having large amounts of wood.
So just harvest trees for wood when really needed (there is no point in having more logs than hearthlings for a start, as they will just carry one block each)