Changing IP subnet of LAN in OpenWrt

This is a small article about changing IP subnet of my LAN while using an OpenWrt router. The main reason I decided to change the IP subnet was that during a travel, when I connected to internet and my home router VPN from a router that had the same subnet as my VPN subnet, the addresses clashed and I could no longer access my home services. So I decided to move from 192.168/16 to 172.16/12 (RFC 1918 Section 3).