I played a world so long with my friends and want to take a little adventure, but we don't want to abandoned our world and to create a new one. So if the mod could allow the existing world generating the cities, how?? also I'm playing with my friends through forge server 1.12.2
please and thank you!

Yes, and I found out how. Contact me on Discord and I will explain it to you.

https://discordapp.com/invite/7QDQRrrZ44 (It's a server so I don't have to share my Discord name on here.)