Reassignment of IP to a device can occur both deliberately (as for example when segmenting or extending your LAN) or inadvertently (as for example when a device on DHCP gets assigned a new IP for some reason). As from my understanding, the only way to reflect such a change in HA is to edit the IP in the config file (homeassisant\config.storage\core.config_entries). If that is indeed true it would IMHO be very useful to be able to reassign IP from the UI.
Also see: WTH are the essential configs of integrations impossible to edit - #13 by KennethLavrsen which extends this topic to other settings besides IP.