Updating OpenWrt on multiboot system

Some time ago I managed to create a multiboot system for OpenWrt and Arch Linux which consisted of creating three partitions, one for Arch Linux and two for OpenWrt - a boot partition and a system partition. That was for 18.06.2. Now I would like to update OpenWrt.
Can I install the latest version on another disk and simply copy the system partition to the system partition of my multiboot system. I assume that the boot partition can remain unchanged.
Is that a valid assumption?